Islamic State group militants have entered a Syrian opposition stronghold in the country's north and are clashing with rebels on the edges of the town.

Syrian opposition groups and IS report that the extremists advanced to the outskirts of Marea Saturday.

The advance — the biggest by IS in Aleppo province in two years — is part of an IS offensive targeting rebel strongholds near the Turkish border that began Thursday night.

On Friday, militants of the group seized six villages in advances that forced the evacuation of a hospital and trapped around 160,000 civilians amid heavy fighting. The advances brought the militants to within three 3 kilometers (2 miles) of the rebel-held town of Azaz and cut off supplies to Marea further south.