BEIRUT - Hundreds of Islamic State fighters have launched an attack on Kurdish forces in northeastern Syria, triggering fierce fighting that has killed dozens on both sides, a group monitoring the war said on Wednesday.
The Kurdish YPG militia, backed by US-led air strikes, had made significant gains in recent weeks against Islamic State in the region, cutting an important supply route from territory controlled by the militant group in Iraq.
Islamic State appeared to try to seize back the initiative on Tuesday, attacking Kurdish forces using tanks and heavy weapons around Ras al-Ayn town near the Turkish border, the Britain-based Syrian Observatory for Human Rights said.
An official in a Kurdish-run defense council in the area also reported heavy clashes in the area of Ras al-Ayn and said the Kurdish forces had been forced to withdraw from a nearby village.
"There are martyrs and dead but the number of martyrs is unknown so far," said the official, speaking via Skype.
The fighting continued into Wednesday. It was not clear exactly how many fighters had been killed on both sides.
The Kurdish campaign in northeastern Syria has been closely coordinated with the US-led coalition that is fighting to roll back Islamic State in Syria and Iraq.