The situation in Kobane in northern Syria remains "dangerous" says US Defence Secretary Chuck Hagel.
Fighting between Islamic State militants and Kurdish defenders continues, with more than 500 people reported dead in a month of conflict.
Mr Hagel said that US-led airstrikes had made progress against the militants, but they still occupied areas on the town's outskirts.
The fight against IS in Syria and Iraq would be a long-term effort, he said.
The BBC reports US aircraft have bombed IS positions as Kurdish fighters cling on to the town's vital border crossing with Turkey.
Mr Hagel, speaking in Chile, said: "We are doing what we can do through our airstrikes to help drive back Isil," as IS is also called.
"In fact there has been some progress made in that area."
Mr Hagel said although the situation in Kobane in northern Syria was very dangerous, the Iraqi military still controlled Baghdad and continued to strengthen their positions there.
At least 553 people are said to have died in a month of fighting for Kobane.
The Syrian Observatory for Human Rights, a UK-based Syrian opposition body which monitors the conflict, counted 298 IS fighters among the total of the dead.
The town's Kurdish defenders say they are outgunned on the ground.
IS offensive fails to take more ground
Kobane resounded to small-arms fire and explosions on Saturday following the failure of a pre-dawn IS offensive to take more ground.
According to the Pentagon, US air strikes on IS targets at Kobane since Friday have hit an IS fighting position; damaged a command and control facility; destroyed a staging building; struck two small units of fighters; and destroyed three lorries.
Mr Nassan said the air strikes had helped the Kurdish fighters regain some territory in the south of the city but they were not enough.
US military teams hold talks with Turkey
Turkey, wary of its recent long conflict with its own large Kurdish population, has ruled out any unilateral ground intervention.
Mr Hagel said that the US had made "considerable progress" in talks with Turkish officials over plans for Turkey to train moderate Syrian rebels and provide them with equipment for their fight against IS militants.
He said US military teams would hold more talks in Turkey in the coming week.
But he declined to comment further, saying he was waiting for Turkey to make its own announcement.
Some 200,000 Syrian Kurdish refugees have crossed the border since the IS advance began nearly a month ago.
Meanwhile, fighting has continued in Iraq, where IS overran large parts of the north during the summer.