The Kurdish People's Protection Units (YPG) announced the "liberation" of Kobani on Monday from the Islamic State (IS) extremist group which seemed poised to seize the town after it began its advance on September 16, AFP said.
Observers say IS lost nearly 1,200 fighters in the battle, of a total of 1,800 killed, 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 Kobani," he added.
With the eyes of the international media watching the militants "wanted to raise the largest flag they ever made over Kobani," the US official said.
"Kobani shows that you're not going to be part of something great .. so the whole narrative that [IS] is trying to put out, Kobani really puts a dent in it,” he added.
Meanwhile, Kurdish fighters continued to battle IS in villages around Kobani, both to the southeast and the southwest, a day after expelling the jihadists from the strategic Syrian town, as thousands of residents who fled across the frontier into Turkey gathered at the border hoping to return, more than four months after the fighting began.