Iranian-backed Iraqi Shiite militia Kataib Hezbollah has threatened to cut the flow of oil to the US after the assassination of an Iranian general.
Qasem Soleimani was killed by a US drone strike on January 3 in Baghdad, Iraq — with the US justifying the attack, saying he posed an "imminent threat" to American lives.
Kataib Hezbollah made the threat in response to remarks by US President Donald Trump that he could impose sanctions on Iraq — after the country's parliament voted to remove US troops from the county.
"If they do ask us to leave, if we don't do it in a very friendly basis. We will charge them sanctions like they've never seen before ever," Mr Trump said.
Abu Ali al-Askari, the security leader of Kataib Hezbollah, responded in a Twitter post that "If Trump the fool imposes economic sanctions on Iraq then we will work with our friends (Iran) to stop the flow of Gulf oil to America."
"Regarding the air base it will be brought to the ground if they (US troops) insist to stay in Iraq," al-Askari said.
Mr Trump also insisted that Iranian cultural sites are fair game for the US military, dismissing concerns within his own administration that doing so could constitute a war crime under international law.
But Congress is pushing back, in what's expected to be a pivotal week as politicians return from a holiday recess.
On Monday, two top Senate Democrats called on Mr Trump to immediately declassify the administration's reasoning for the strike on the Iranian official, Gen. Qassem Soleimani, saying there is "no legitimate justification" for keeping the information from the public.
House Speaker Nancy Pelosi said late Sunday the House would introduce and vote this week on a war powers resolution to limit the president's military actions regarding Iran.
In a letter to House Democrats, Ms Pelosi called the air strike "provocative and disproportionate" and said it had "endangered our servicemembers, diplomats and others by risking a serious escalation of tensions with Iran."
A similar resolution was introduced in the Senate.
Congress, which has the sole power to declare war, has complained that Mr Trump did not provide advance notice of his decision to strike in Iraq.
Mr Trump did meet the 48-hour deadline required by the War Powers Act to notify Congress after the deadly drone strike, though the document was classified and no public version was released.
The administration is expected to brief politicians on its actions this week.
In their letter to Mr Trump, Senate Minority Leader Chuck Schumer of New York and the Senate Foreign Relation Committee's Sen. Robert Menendez of New Jersey said the White House's classified notification sent to Congress late Saturday under the War Powers Act was insufficient and inappropriate.
"It is critical that national security matters of such import be shared with the American people in a timely manner, they wrote.
Iran has vowed to retaliate for Mr Trump's targeted killing of Gen Soleimani, the head of Iran's elite Quds force. It has sparked outrage in the Middle East, including in Iraq, where more than 5,000 American troops are still on the ground 17 years after the US invasion. Iraq's parliament voted Sunday in favour of a nonbinding resolution calling for the expulsion of the American forces.
Trump first raised the prospect of targeting Iranian cultural sites Saturday in a tweet. Speaking with reporters Sunday as he flew back to Washington from his holiday in Florida, he refused to back down, despite international prohibitions.
"They're allowed to kill our people. They're allowed to torture and maim our people.
"They're allowed to use roadside bombs and blow up our people. And we're not allowed to touch their cultural sites? It doesn't work that way," Mr Trump said.
On Iraq, Mr Trump said the US wouldn't leave Iraq without being paid for its military investments there over the years - then said if the troops do have to withdraw, he would hit Baghdad with economic penalties.
"We will charge them sanctions like they've never seen before ever. It'll make Iranian sanctions look somewhat tame," he said. "If there's any hostility, that they do anything we think is inappropriate, we are going to put sanctions on Iraq, very big sanctions on Iraq." He added: "We're not leaving until they pay us back for it." The administration has scrambled to contend with the backlash to the killing of Gen Soleimani, which marked a stark escalation in tensions between Washington and Tehran.
MORE STRIKES
Secretary of State Mike Pompeo said the US military may well strike more Iranian leaders if the Islamic Republic retaliates. He tip-toed around questions about Mr Trump's threat to attack Iranian cultural sites, a military action that likely would be illegal under the laws of armed conflict and the UN charter. Mr Pompeo defended the targeted killing of Gen Soleimani, saying the administration would have been "culpably negligent" in its duty to protect the United States if it had not killed him.
He did not provide evidence for his previous claims that Gen Soleimani was plotting imminent attacks on Americans. Instead of arguing that an attack had been imminent, Mr Pompeo said it was inevitable.
WAR CRIMES?
Trump's threat to attack cultural sites, rattled some administration officials. One US national security official said the president had caught many in the administration off guard and prompted internal calls for others in the government to clarify the matter. The official, who was not authorised to speak publicly to the issue, said clarification was necessary to affirm that the US military would not intentionally commit war crimes.
Oona Hathaway, an international law professor at Yale and a former national security law official in the Defense Department's legal office, said Mr Trump's threat amounted to "a pretty clear promise of commission of a war crime." The president's threats to Iran did little to quell Tehran's furore over the death of Gen Soleimani. Iranian state television reported that the country would no longer abide by any limits of the 2015 nuclear deal it signed with the United States and other world powers. Mr Trump withdrew the US from the deal in 2018 and stepped up economic sanctions on Tehran, actions that accelerated a cycle of hostilities leading to the last week's killing.
These Media Posts will serve as notification to the United States Congress that should Iran strike any U.S. person or target, the United States will quickly & fully strike back, & perhaps in a disproportionate manner. Such legal notice is not required, but is given nevertheless!
Mr Schumer said he worried that "the actions the president took will get us into what he calls another endless war in the Middle East. He promised we wouldn't have that."
Mr Schumer said Mr Trump lacks the authority to engage militarily with Iran and Congress needs a new war powers resolution "to be a check on this president."
To which Mr Pompeo said: "We have all the authority we need to do what we've done to date."
Mr Trump made clear Sunday that he saw little reason to give Congress advanced warning if he orders the military to carry out further actions against Iran. "These Media Posts will serve as notification to the United States Congress that should Iran strike any US person or target, the United States will quickly & fully strike back, & perhaps in a disproportionate manner," he wrote on Twitter. "Such legal notice is not required, but is given nevertheless!" In response, the House Foreign Affairs Committee tweeted: "This Media Post will serve as a reminder that war powers reside in the Congress under the United States Constitution. And that you should read the War Powers Act. And that you're not a dictator." Some Democrats running to challenge Mr Trump in November questioned whether he had a long-term plan for the Mideast.
Former Vice President Joe Biden said Mr Trump was ill-prepared for the repercussions of the strike on Gen Soleimani and had alienated allies by not alerting them of the plans. Pete Buttigieg, the former mayor of South Bend, Indiana, said, "When you're dealing with the Middle East, you need to think about the next and the next and the next move. This is not checkers."
Gen Soleimani's successor, Esmail Ghaani stood near Khamenei's side, as did Iranian President Hassan Rouhani and other top leaders in the Islamic Republic. While Iran recently faced nationwide protests over government-set gasoline prices that reportedly killed over 300 people, Gen Soleimani's mass processionals has seen politicians and leaders across the Islamic Republic's political spectrum take part, temporarily silencing that anger.
Demonstrators burned Israeli and US flags, carried a flag-draped US coffin or effigies of Mr Trump. Some described Mr Trump himself as a legitimate target for Iran's revenge.
Mohammad Milad Rashidi, a 26-year-old university graduate, predicted more tension ahead.
"Trump demolished the chance for any sort of possible agreement between Tehran and Washington," Rashidi said. "There will be more conflict in the future for sure." Ghaani made his own threat in an interview with Iranian state television aired Monday. "God the Almighty has promised to get his revenge, and God is the main avenger. Certainly actions will be taken," he said.
Weeping amid wails from a sea of mourners, Iran's supreme leader on Monday prayed over the remains of a top Iranian general killed in a US air strike in Baghdad, an attack that's drastically raised tensions between Tehran and Washington.
The targeted killing of the Iranian Revolutionary Guard Gen. Qassem Soleimani drew a crowd, said by police to be in the millions, on Monday in Tehran, where Gen Soleimani's replacement vowed to take revenge. Additionally, Tehran has abandoned the remaining limits of its 2015 nuclear deal with world powers in response to the slaying while in Iraq, the parliament has called for the expulsion of all American troops from Iraqi soil.
The developments could bring Iran closer to building an atomic bomb, set off a proxy or military attack launched by Tehran against America and enable the Islamic State group to stage a comeback in Iraq, making the Middle East a far more dangerous and unstable place.
Adding to the tensions, President Donald Trump threatened to demand billions of dollars in compensation from Iraq or impose "sanctions like they've never seen before" if it goes through with expelling US troops.
Gen Soleimani's daughter, Zeinab, directly threatened an attack on the US military in the Mideast while speaking to a crowd that stretched as far as the eye could see down major thoroughfares in Iran's capital.
"The families of the American soldiers in western Asia ... will spend their days waiting for the death of their children," she said to cheers. Iranian state television and others online shared a video that showed Mr Trump's American flag tweet following Gen Soleimani's killing turn into a coffin, the "likes" of the tweet replaced by over 143,000 "killed" with the hashtag #severerevenge. Iran's Supreme Leader Ayatollah Ali Khamenei himself prayed over the caskets of Gen Soleimani and others slain in the attack. Khamenei, who had a close relationship with Gen Soleimani, wept at one point during the traditional Muslim prayers for the dead. The crowd wailed.
Gen Soleimani's successor, Esmail Ghaani stood near Khamenei's side, as did Iranian President Hassan Rouhani and other top leaders in the Islamic Republic. While Iran recently faced nationwide protests over government-set gasoline prices that reportedly killed over 300 people, Gen Soleimani's mass processionals has seen politicians and leaders across the Islamic Republic's political spectrum take part, temporarily silencing that anger.
Demonstrators burned Israeli and US flags, carried a flag-draped US coffin or effigies of Mr Trump. Some described Mr Trump himself as a legitimate target for Iran's revenge.
Mohammad Milad Rashidi, a 26-year-old university graduate, predicted more tension ahead.
"Trump demolished the chance for any sort of possible agreement between Tehran and Washington," Rashidi said. "There will be more conflict in the future for sure." Ghaani made his own threat in an interview with Iranian state television aired Monday. "God the Almighty has promised to get his revenge, and God is the main avenger. Certainly actions will be taken," he said.
MARKETS REACT
Markets reacted Monday to the tensions, sending international benchmark Brent crude above $70 a barrel. The Middle East remains a crucial source of oil and Iran in the past has threatened the Strait of Hormuz, the narrow mouth of the Persian Gulf through which 20 per cent of all the world's oil traded passes. Ghaani, a longtime Gen Soleimani deputy, has now taken over as the head of the Revolutionary Guard's Quds Force, an expeditionary arm of the paramilitary organisation answerable only to Khamenei. Ghaani has been sanctioned by the US since 2012 for his work funding its operations around the world, including its work with proxies in Iraq, Lebanon and Yemen.
Those proxies likely will be involved in any operation targeting US interests in the Mideast or elsewhere in the world.
Already, the US Embassy in Saudi Arabia warned Americans "of the heightened risk of missile and drone attacks." In Lebanon, the leader of the Iranian-backed militant group Hezbollah said Gen Soleimani's killing made US military bases, warships and service members across the region fair game for attacks. A former Iranian Revolutionary Guard leader suggested the Israeli city of Haifa and others could be targeted should the US attack Iran.
"We promise to continue down martyr Gen Soleimani's path as firmly as before with help of God, and in return for his martyrdom we aim to get rid of America from the region," Ghaani said.