Kurdish fighters along with Arab allies have recaptured the town of Shaddadi, the last stronghold of Islamic State in Syria's north-eastern al-Hassakeh province, a monitoring group said Friday.
Intense battles pitting the People's Protection Units (YPG) and Arab allies against Islamic State militants had raged since early Wednesday in the town before it was retaken, the Syrian Observatory for Human Rights reported.
"The operation was carried out under the cover of the US-led airstrikes and supported by American officers," Rami Abdel Rahman, head of the Britain-based observatory, told dpa.
Islamic State had been present for the last two years in Shaddadi, on the southern outskirts of al-Hassakeh.
YPG, backed by an intense US-led air campaign, has been the main force pushing back jihadists across northern Syria.
UN special envoy to Syria Staffan de Mistura said peace talks will not resume on February 25, while the observatory reported ongoing ground battles despite a pledge by world powers to bring about a "cessation of hostilities" by Friday.
"I cannot realistically call new Geneva talks for February 25. We need 10 days of preparation and invitations. But we aim to do so soon," de Mistura told Swedish daily Svenska Dagbladet in an interview published Friday.
Earlier this month, de Mistura put the Geneva peace talks on hold until February 25, saying military action had created an obstacle to the negotiations.
"We need real talks about peace, not just talks about talks," he said in the telephone interview from Damascus. "Now the Americans and Russians must sit down and agree on a concrete plan on the cessation of hostilities."
De Mistura was unsure when he would call talks: "We have been disappointed in the past - now I am pragmatic and determined."
The envoy said that he wanted the United States and Russia, with their partners, to "agree about a beginning of a cessation of hostilities between today and the middle of next week. Now the ball is in their court."
In Washington, US State Department spokesman Mark Toner said it was "incumbent on Russia to exert influence just as it is incumbent of the other members of [the International Syria Support Group] where they have influence, to ... exert that influence to the forces on the ground, to lay down their arms, to stop fighting each other."
The cessation of hostilities was proposed last week by world powers meeting in Munich. Part of the plan was to ensure access for humanitarian aid to besieged populations in Syria.
"We did not see any changes on the ground. ... Battles, shelling and raids go on," Abdel Rahman said. "Nothing indicates there is a cessation of hostilities."
In another development, warplanes believed to be Russian carried out consecutive raids on areas in the southern province of Daraa and on the outskirts of the capital, Damascus.