Islamic State jihadists boasted Thursday they had executed scores of Syrian troops after capturing a key air base, the latest in a string of abuses that have shocked the world.
News of the killings came as US President Barack Obama weighed air strikes on IS positions in Syria and edged closer to greenlighting a mission to aid Shiite Turkmen trapped in an Iraqi town besieged by the jihadists.
It also came as rival Islamist rebels led by Al-Qaeda affiliate Al-Nusra Front seized 43 UN peacekeepers on the Golan Heights, part of a mission that has monitored an armistice between Syrian and Israeli troops on the strategic plateau for decades. All the forces were from Fiji.
The UN Security Council condemned the action and demanded the "unconditional and immediate release" of the peacekeepers, a statement said.
Obama administration officials said on Wednesday said US is intensifying its push to build an international campaign against Islamic State jihadist fighters in Iraq and Syria, including recruiting partners for potential joint military action, .
Britain and Australia are potential candidates, U.S. officials said. Germany said on Wednesday it was in talks with the United States and other international partners about possible military action against Islamic State but made clear it would not participate.
Washington has so far baulked at cooperating with Damascus against the jihadists.
IS posted grisly video footage on the Internet of scores of bodies heaped in the desert they boasted were those of Syrian soldiers they captured and executed following its seizure of Tabqa air base.
The jihadists have repeatedly posted gruesome videos, which have appalled international opinion but served as a propaganda tool to recruit volunteers.
Britain-based monitoring group the Syrian Observatory for Human Rights said that IS had executed at least 160 soldiers, among some 500 who had made a desperate bid to escape to government-held territory after their defeat last Sunday.