Zeina Karam

BEIRUT: Islamic State militants entered a major Syrian opposition stronghold in the country’s north on Saturday, clashing with rebels on the edges of the town as the extremist group builds on its most significant advance near the Turkish border in two years — even as it loses ground elsewhere in the country and in neighboring Iraq.

The town of Marea, just north of Aleppo city, has long been considered a bastion of relatively moderate Syrian revolutionary forces fighting to topple Assad. The IS assault underlined the weakness of the groups fighting under the loose banner of the so-called Free Syrian Army that have been struggling to survive.

More than 160,000 civilians have been trapped by the fighting, which also forced the evacuation of one of the few remaining hospitals in the area, run by the international medical organization Doctors Without Borders.

On Saturday, IS fighters staged two suicide bombings targeting “opposition forces” near Marea, IS said via its news agency, Aamaq.

Following the suicide bombings, IS militants entered Marea and fighting began inside the town, according to the Syrian Observatory for Human Rights, a Britain-based opposition media outfit that tracks Syria’s civil war.

Dr. Abdel Rahman Alhafez, who heads one of the last remaining hospitals in Marea, said the town was encircled and his hospital under threat since Friday. “We need urgent protection for the hospital or a way out,” he said in an emailed statement.

Syrian army warplanes and helicopters, meanwhile, pounded other opposition-held towns in Aleppo province on Saturday, putting a further strain on embattled rebels fighting President Bashar Assad’s forces.

Islamic State’s territorial gains around Marea and Azaz, both critical rebel bastions north of the city of Aleppo, are a blow to the Turkey- and Saudi-backed opposition fighters who have been struggling to retain a foothold in the region while being squeezed by opponents from all sides. They also demonstrated the IS group’s ability to stage major offensives and capture new areas, despite a string of recent losses in Syria and Iraq.

American Special Operations forces and a coalition of Syrian and Arab fighters known as the Syria Democratic Forces have begun clearing areas north of Raqqa, the Islamic State’s de facto capital in Syria, in preparation for an eventual assault on the city.

The IS offensive targeting Syrian opposition strongholds near the Turkish border began on Thursday night.

On Friday, militants of the group captured six villages near Azaz, triggering intense fighting that trapped tens of thousands of civilians unable to flee to safety while Turkey’s border remains closed. A few hundred fled west to the Kurdish-held enclave of Afrin.

People are “terrified for their lives,” the International Rescue Committee said in a statement. The group said it has received confirmed reports that at least four entire families, including children, were killed Friday on the outskirts of Azaz.

The IRC runs centers for both children and women in Azaz and provides clean water and sanitation to a camp supporting 8,500 people. More than half the camp’s population has left to find safety elsewhere in the town, it said. The IRC also relocated its staff from the centers and the camp to safer areas of Azaz until the situation enables them to return.

The U.N. refugee agency said it was “deeply concerned” about the fighting affecting thousands of vulnerable civilians.

“Fleeing civilians are being caught in crossfire and are facing challenges to access medical services, food, water and safety,” it said in a statement Saturday.

The advances brought the militants to within a few miles of the rebel-held Azaz and cut off supplies to Marea further south.