Large numbers of foreign fighters are among the ISIS jihadists killed in the battle for the Syrian town of Kobane, a senior US official said Tuesday, saying the concerted campaign was halting the Islamists' march.
The Kurdish People's Protection Units (YPG) announced the "liberation" of Kobane on Monday, depriving the Islamic State group of a strategic prize to add to its territory in Syria and Iraq.
The United States says Kurdish fighters are now in control of about 90 percent of the town on the Syrian-Turkish border.
"ISIL is now, whether on order or whether they are breaking ranks, is beginning to withdraw from the town," a senior State Department official told reporters, using another term for ISIS.
But he warned that the terrorists were "adaptive and resilient" and no-one was declaring "mission accomplished" yet.
The US and some 60 coalition partners is engaged in the "first phase of a multi-year campaign," he stressed.
But a victory in Kobane was an important milestone in trying to change "the narrative" of the jihadists who have attracted thousands of foreign fighters to their ranks, mostly disaffected youth drawn by the promise of adventure.
ISIS had poured some of its best foreign fighters into Kobane, the State Department official said, but in the last six weeks the losses had begun to cause splits in the ranks.
The group has even executed foreign fighters for refusing orders to deploy to the town.
Observers say ISIS lost nearly 1,200 fighters in the battle, out of a total of 1,800 killed in total, despite outgunning YPG forces with sophisticated weaponry captured from Iraqi and Syrian military bases.
"We don't get into body counts, but it's in the four figures in terms of the overall number of ISIL fighters that have been killed," the State Department official confirmed.
Many foreign fighters - many of them Australians, Belgians, Canadians and Chechens - were among them, he said, refusing to give exact figures other than to say "it was hugely, hugely significant."
"The entire notion of this organization which is on the march, inevitable expansion, (its) overall momentum has been halted at Kobane," he added.
The US began airstrikes on ISIS to stop its march on Kobane in September and in October airdropped in critical supplies to the anti-ISIS fighters.
Washington also worked with Turkey to open a land corridor to allow Kurdish Peshmerga fighters from northern Iraq's autonomous Kurdish region to help defend the beleaguered town.
With the eyes of the international media watching the jihadists "wanted to raise the largest flag they ever made over Kobane," the US official said.
"Kobane shows that you're not going to be part of something great... so the whole narrative that ISIL is trying to put out, Kobane really puts a dent in it."