Damascus, Aug 29 (IANS): The Islamic State (IS) militants killed more than 160 Syrian soldiers captured by them in Syria's northern province of al-Raqqa, activists said.

The militants captured the Syrian soldiers while fleeing the al-Tabaqa airbase when the airbase was recently seized by the IS, Xinhua reported citing the Britain-based Syrian Observatory for Human Rights Thursday.

According to a video footage, ten Syrian soldiers stripped off their uniforms and herded in their underwear only toward an unknown location where the militants started summarily executing them.

Other activists placed the number of the slain soldiers at 250.

On Aug 24, the Syrian troops evacuated their positions at the airbase after intense battles with the militants, who captured the facility.

The airbase was the last standing stronghold for the Syrian troops in al-Raqqa, which has largely fallen to the IS fighters since a year ago.

The Islamic State, previously known as the Islamic State in Iraq and Syria, has recently proclaimed to establish an "Islamic Caliphate" in parts of Syria and Iraq, threatening the political geography in the region.

The group, believed to be 70,000 fighters strong, is led by Abu Bakr al-Baghdadi.