Opposition fighters in northwestern Syria's Idlib have repelled an infiltration attempt by the Bashar Assad regime forces, Anadolu Agency reported Friday.

According to local sources, the regime military withdrew from the southern parts of Idlib and the outskirts of the northern town of Hama after heavy clashes on Thursday night. The sources added that regime troops suffered heavy losses during the offensive.

Earlier this year, Syrian troops launched an offensive on Idlib that lasted four months.

According to Syria's Response Coordination Group, a local nongovernmental organization, some 40,000 civilians within the Idlib de-escalation zone were displaced by attacks carried out by the regime and its ally, Russia, in the first half of November.

Last September, Turkey and Russia agreed to turn Idlib into a de-escalation zone where acts of aggression are expressly prohibited. The Syrian regime and its allies, however, have consistently broken the terms of the cease-fire, launching frequent attacks inside the zone.

The de-escalation zone is currently home to some 4 million civilians, including hundreds of thousands displaced in recent years by regime forces from throughout the war-weary country.

Syria has been locked in a vicious civil war since early 2011 when the regime cracked down on pro-democracy protests with unexpected ferocity. Since then, hundreds of thousands of people have been killed and more than 10 million others displaced, according to U.N. officials.