BEIRUT (Reuters) - Islamic State fighters stormed a Syrian town held by Kurdish-led forces near Raqqa city on Monday, part of a wider offensive by the militants two days after their de facto capital was hit by some of the heaviest U.S.-led air strikes in the conflict.
The Kurdish YPG militia said it was fighting to expel Islamic State fighters who had attacked Ain Issa, captured from them only two weeks ago with aerial support from the U.S.-led military alliance. Ain Issa sits on a major east-west highway from Aleppo in the west to the Iraqi city of Mosul.
Defense Secretary Ash Carter said on Monday a flurry of U.S. air strikes around Raqqa over the weekend was aimed at disrupting the ability of Islamic State fighters to parry advances by Kurdish forces.
Carter, speaking at a news conference with French Defense Minister Jean-Yves Le Drian, said air strikes targeting bridges and Islamic State positions around its declared capital of Raqqa were aimed at limiting the group's "freedom of movement and ability to counter those capable Kurdish forces."
The Syrian Observatory for Human Rights, which reports on the war, said Islamic State forces had taken Ain Issa and areas around it some 50 km (30 miles) north of Raqqa city. Air strikes at the weekend destroyed seven bridges over waterways in Raqqa, which is bordered to the south by the Euphrates river, it said.
The monitor said at least 37 Islamic State fighters were killed and scores wounded in air strikes by the coalition and in clashes with Kurdish militia in the last twenty four hours in northeastern Syria.
It said sources on the ground confirmed the figures from the bodies of fighters and injured militants arriving since Sunday night at hospitals in the de facto capital of the militants in Raqqa city.[L8N0ZM39U]
Monday's attack on Ain Issa was part of a coordinated Islamic State offensive on YPG positions that also targeted the northeastern province of Hasaka, bordering Turkey to the north and Iraq to the south, YPG spokesman Redur Xelil said.
The YPG has been the only notable partner to date on the ground in Syria for the U.S.-led alliance battling to eliminate Islamic State in Syria and northern Iraq, where the group has declared a "caliphate" to, in its terms, rule over all Muslims.
YPG-led forces said they had captured Ain Issa on June 23 in part of an offensive that drove deep into Islamic State's stronghold of Raqqa province. They also said they had captured the northern town of Tel Abyad at the Turkish border.
In the last two days, Islamic State have attacked YPG-held positions near the northeastern city of Hasaka, which is divided between government and YPG control, a Kurdish official in Hasaka province said. Hasaka is important not least for its location at the border with territory controlled by Islamic State in Iraq.
The Observatory said the Islamic State offensive stretched all the way from Hasaka province in the north east to the town of Sarin in the north western Aleppo province.
"It is an important victory for Daesh," said Rami Abdul Rahman, head of the Observatory, using an Arabic acronym for Islamic State.
Amaq News Agency, which supports Islamic State militants, said the group's fighters had been able in a surprise assault to regain large parts of the Raqqa and Hasaka countryside, including Ain Issa.
Additional reporting by Sylvia Westall, David Alexander in Washington and Mostapha Hashim in Cairo; Writing by Tom Perry; Editing by Ralph Boulton