US officials have been saying for several months that US airstrikes were degrading Isis fighters in Iraq and the radical Sunni group, under pressure from Iraqi forces, had lost as much as 25 per cent of the territory it gained during its blitzkrieg last year.
A large offensive involving the Iraqi Army, Sunni tribal fighters and American airstrikes was supposed to begin soon in western Iraq's Anbar province, where Ramadi is the provincial capital.
The unexpected collapse of Iraqi forces in Ramadi, including elite counterterrorism troops from Iraq's Golden Division, suggests the Iraqi forces may be weaker than many in the US Government thought. The recent battlefield setbacks also point to a broader challenge facing the Obama Administration's campaign against Isis throughout the Middle East.
The President has insisted only local ground forces, bolstered by US training and air power, can defeat Isis fighters who have gained ground and new recruits in Yemen, Libya, Syria and Iraq.
But finding local partners, especially Sunnis, in a region that is being torn apart by unprecedented levels of sectarian fighting has proved difficult.
"The really important question moving forward is how do we find effective partners - not just in Iraq but in Syria and in Yemen and in Libya - that we can work with," Obama said in a recent interview. That has proved particularly vexing in Iraq, where Sunni tribesmen have been largely unwilling to battle Isis on behalf of a Shia-dominated Government they think is out to oppress them.
Senator John McCain said that more support from the US military, in the form of extra US Special Operations troops who would accompany Iraqi troops into battle, could bolster the will of the Iraqi ground forces.
Frontline combat advisers, who would be at greater risk of death or injury from enemy fire than current American trainers, could strengthen the resolve of untested Iraqi troops, a senior US official said, like "the steel rod up the backbone".
Special Ops advisers could also direct airstrikes from American warplanes, improving accuracy.
Obama Administration officials have suggested more US airstrikes would not necessarily change the performance of Iraqi troops.
"Airstrikes are effective, but neither they nor really anything we do can substitute for the Iraqi forces' will to fight. They're the ones who have to beat [Isis] and keep them beaten," Carter said.
Iraqi politicians hit back at Carter's claims, and fighters who fled Ramadi said that more US airstrikes would have enabled them to keep control of the city.
217 executed by Isis: report
Isis has executed at least 217 people, including children and their parents, in and around the ancient Syrian city of Palmyra.
The Syrian Observatory for Human Rights says it has documented the executions of 67 civilians, including children, and 150 regime forces by Isis in different parts of Homs province since May 16.
The Observatory said the executions came in the days after Isis began a sweep into Homs from their stronghold in neighbouring Deir Ezzor province. They captured Sukhnah and then Palmyra, prompting international concern about the fate of the city's ancient ruins. The Observatory said another 600 people had been taken prisoner by Isis in their sweep through the area.
- Washington Post-Bloomberg, AFP