DAMASCUS — Militants fighting the Syrian army have detained 43 U.N. peacekeepers in the Israeli-occupied Golan Heights and trapped another 81 in the region, and the world body is working to secure their release, the United Nations said on Thursday.

The affected peacekeepers are from the Philippines and Fiji, U.N. spokesman Stephane Dujarric told reporters.

“During a period of increased fighting beginning yesterday between armed elements and Syrian Arab Armed Forces within the area of separation in the Golan Heights, 43 peacekeepers from the United Nations Disengagement Observer Force (UNDOF) were detained early this morning by an armed group in the vicinity of Al Qunaytirah,” the U.N. press office said in a statement.

It added that another 81 UNDOF peacekeepers were being restricted to their positions in the vicinity of Ar Ruwayhinah and Burayqah. Dujarric said the 81 trapped troops were from the Philippines and the 43 seized ones from Fiji.

Britain’s U.N. Ambassador Mark Lyall Grant, president of the Security Council this month, told reporters the trapped peacekeepers were surrounded by Islamist militants.

The 15-nation Security Council, which was meeting on the humanitarian situation in Syria, was also discussing the issue of the kidnapped peacekeepers, Lyall Grant said.

The council later issued a statement strongly condemning the seizure of the peacekeepers and calling for their immediate release. U.N. Secretary-General Ban Ki-moon echoed the council word’s in his own statement of condemnation.

U.N. officials say that the peacekeepers, whose job is to monitor the cessation of hostilities, carry small arms that are only to be used in extreme circumstances. In previous situations where UNDOF peacekeepers were held hostage, the troops did not use their weapons.

The Quneitra crossing on the Golan is a strategic plateau captured by Israel in a 1967 Middle East war. Syria and Israel technically remain at war. Syrian troops are not allowed in an area of separation under a 1973 ceasefire formalized in 1974.

UNDOF monitors the area of separation, a narrow strip of land running about 45 miles (70 km) from Mount Hermon on the Lebanese border to the Yarmouk River frontier with Jordan. There are 1,223 UNDOF peacekeepers from six countries.

The United Nations said this week that the Philippines has decided to pull out of UNDOF, and from a U.N. force in Liberia, which is struggling with an outbreak of the deadly Ebola virus.

Blue-helmeted U.N. troops were seized by militants in March and May 2013. In both of those cases they were released safely.

Austria, Japan and Croatia have all pulled their troops out of UNDOF due to the deteriorating security situation and spillover from the Syrian war.

Islamic State fighters executed scores of Syrian soldiers captures when the militants seized an airbase in the province of Raqqa at the weekend, according to a video posted on YouTube on Thursday.

The video, confirmed as genuine by an “Islamic State” fighter, showed the bodies of dozens of men lying face down wearing nothing but their underwear. They were stretched out in a line that appeared to be dozens of meters long.

A separate pile of bodies was shown nearby. Reuters could not independently verify the authenticity of the video.

The caption beneath it said the dead numbered 250. An “Islamic State” fighter in Raqqa told Reuters via the Internet: “Yes, we have executed them all.”

The Syrian Observatory for Human Rights, which monitors violence in the war, put the death toll at more than 120.

“Islamic State,” a radical offshoot of al Qaeda, stormed Tabqa airbase on Sunday after days of clashes with the army and said it had captured and killed soldiers and officers in one of the bloodiest confrontations yet between the two sides.

The capture of Tabqa, the Syrian army’s last foothold in that area, and apparent parading and killing of large numbers of its soldiers shows how “Islamic State” has cemented its grip on the north of the country.

The video begins by showing the captives apparently being marched in the desert with their hands behind their heads and watched by armed men. An “Islamic State” fighter repeatedly shouts out “Islamic State,” to which the men reply “It shall remain.”

President Obama tamped down the prospect of imminent U.S. military action in Syria on Thursday, saying “we don’t have a strategy yet” for degrading the “Islamic State.”

The president spoke shortly before convening a meeting of his national security advisers to discuss a range of Pentagon options for confronting the “Islamic State.” The U.S. is already striking militant targets in Iraq and administration officials have said the president was considering similar action in neighboring Syria.

The described the militants as an “immediate threat” to Iraq and the region.

He ruled out the possibility of coordinating U.S. airstrikes in Syria with Assad’s government. He added that the United State did not “have to choose” between Assad and the militants.

Obama reiterated his stand that Assad has lost his legitimacy.