BEIRUT, Lebanon (AP) — The Islamic State group killed more than 160 Syrian government troops seized in recent fighting, posting pictures of terrified young conscripts stripped down to their underwear before meeting their deaths in the arid Syrian countryside.

The images of the slayings that emerged yesterday were the latest massacre attributed to the extremist group, which has terrorised rivals and civilians alike with widely publicised brutality in Syria and Iraq as it seeks to expand a proto-state it has carved out on both sides of the border.

In southern Syria, meanwhile, gunmen detained 43 UN peacekeepers during fighting on the Syrian side of the Golan Heights, the United Nations said. It added that another 81 peacekeepers were trapped in the area by heavy clashes between rebels and Syrian troops.

The mass killing of Syrian soldiers is part of a stepped up campaign by Islamic State militants targeting President Bashar Assad’s forces. Until recently, the group had been focused on eliminating rivals among the rebels fighting to topple him, systematically routing Western-backed opposition fighters and other Islamic factions from towns and villages in northern and eastern Syria as it expands.

More recently, the jihadists have turned their attention to Assad’s forces, seizing a series of military bases in northeastern Raqqa province. In the process, they have killed hundreds of pro-government forces, beheading some and later displaying their severed heads on poles and fences and posting the pictures online.

Most of the dozens killed over the past 24 hours were rounded up Wednesday near the Tabqa airbase, three days after Islamic State fighters seized the base. The government troops were among a large group of soldiers from the base who were stuck behind front lines after the airfield fell to the jihadi fighters.

A statement posted online and circulated on Twitter claimed the extremists killed about 200 government prisoners captured near Tabqa. It also showed photographs of what it said were the prisoners: young men stripped down to their underwear marching in the desert, some with their hands behind their heads. The photos could not immediately be verified, but correspond to other AP reporting.

The group also posted a video showing Islamic State fighters forcing the barefoot men to march through the desert. Another video later showed dozens of bodies piled in the desert, alongside others lying motionless — apparently dead — in a row in the sand.

While the videos could not be independently confirmed by the AP, they appeared to illustrate the claims made online by the Islamic State group and Syrian opposition activists about the mass killing.