Beirut: Islamic State group fighters seized five villages from rebel forces in Syria`s northern Aleppo province overnight and entered the outskirts of a key opposition bastion there, a monitor said Thursday.
The jihadist group seized three villages near the town of Marea and entered its southern outskirts, the Britain-based Syrian Observatory for Human Rights said.
IS fighters took another two villages further north in Aleppo province, near the border with Turkey.
Those two villages were previously controlled by Al-Nusra Front, Al-Qaeda`s Syrian affiliate, which withdrew from them after Turkey and the United States announced plans to cooperate on an IS-free zone in the area.
Marea is one of the most significant rebel-held towns in northern Aleppo and lies on a key supply route running to the Turkish border.
IS has targeted the town for months, seeking to expand westwards from territory it already holds in Aleppo province.
The Observatory said there were reports of dozens of rebel casualties in the fighting, but it had no immediate toll.
It also reported an IS car bomb on the southern outskirts of Marea on Thursday morning, but had no details on deaths or injuries.
Activists and medical organisations said this week they had documented an alleged chemical weapons attack, possibly involving mustard gas, on the town last Friday. Activists accused IS of being behind the attack.
The IS advances come despite an agreement between Turkey and the United States to work on the establishment of an IS-free zone in northern Aleppo.
The plan has backing from some rebel forces on the ground, including the powerful Islamist Ahrar al-Sham movement, which Washington does not work with.
But Al-Nusra has rejected the proposal, despite its opposition to IS, and earlier this month withdrew from its front lines against its jihadist rival in Aleppo in order to avoid cooperating with the plan.
It turned those positions over to other rebels.
More than 240,000 people have been killed in Syria since the conflict began in March 2011 with peaceful anti-government protests.
It has evolved into a complex multi-front war, with regime and rebel forces as well as Kurds and jihadists involved in the fighting, and a US-led coalition carrying out air strikes against IS.