The US military acknowledged for the first time yesterday that it launched an airstrike against Isis in the densely packed Iraqi city of Mosul, where residents say more than 100 people were killed in a single event.
If confirmed, the March 17 incident would mark the greatest loss of civilian life since the US began strikes on Isis (Islamic State) targets in Iraq and Syria in 2014.
An "initial review" showed that the coalition struck Isis fighters and equipment in west Mosul at the request of Iraq forces and "at the location corresponding to allegations of civilian casualties," the task force leading the coalition said.
"We are stunned by this terrible loss of life," said Lise Grande, the UN's Iraq coordinator.
It comes after the Trump Administration pledged to relax its rules of engagement to "unshackle" its forces in Iraq.
Earlier this month, Sebastian Gorka, the President's deputy assistant, said: "We are going to unshackle our guys. We're going to remove the incredible, suicidal rules of engagement.
"We're not going to employ the 8000 mile screwdriver which they inherited from Vietnam ... the idea that you are not allowed to target an Isis convoy unless somebody in Washington on a live video feed signs off on it - that's insanity."
The pause on retaking the city, a key battleground for Isis, came as civil defence officials warned that many residents were still trapped under rubble in al-Jadidah district.
According to residents and local activists, the air strike detonated an Isis truck loaded with explosives which destroyed several buildings, leading to major civilian casualties.
The US is also looking into a similar incident in Syria on March 16, when an air strike killed dozens of civilians.
US defence officials said the attack in Syria was on a known meeting place for members of al-Qaeda, but it later emerged that the building was near a mosque in Jinna, Aleppo province.
"In Jinna, the attack on the mosque killed 35 civilians, and six of those were children," said Rami Abdurrahman, of the Syrian Observatory for Human Rights. "There was an attack on a bakery in Al-Tabqa that killed 19 civilians.
The civilian casualties are increasing."
The US-backed offensive to drive Isis out of Mosul, now in its sixth month, has recaptured the eastern side of Mosul and about half of the west.
But advances have stuttered in the past two weeks as fighting enters the narrow alleys of the Old City, home to the al-Nuri mosque where Isis leader Abu Bakr al-Baghdadi declared a caliphate spanning swathes of Iraq and Syria in 2014.
