BEIRUT — New video Thursday of UN peacekeepers held captive by Syrian rebels illustrates the sudden vulnerability of a UN force that had patrolled a cease-fire line between Israel and Syria without incident for nearly four decades.
The abduction of the Filipino troops — soft targets in Syria’s civil war — also sent a worrisome signal to Israel about the lawlessness it fears along the shared frontier if Syrian President Bashar Assad is ousted.
Opposition fighters seized the 21 peacekeepers Wednesday near the Syrian village of Jamlah just a mile from the Israeli-controlled Golan Heights, a plateau Israel captured from Syria in 1967.
Negotiations were underway Thursday for the release of the men, who said in videos posted online that they were being treated well.
However, a rebel spokesman seemed to suggest the hostages were also serving as human shields. If the UN troops are released and leave the area, the regime could kill ‘‘as many as 1,000 people,’’ said the spokesman, who spoke via Skype and did not give his name for fear of reprisals.
The peacekeepers’ abduction highlights the growing risks to UN staff in Syria’s escalating conflict.
Fighting has spread across the country, claiming more than 70,000 lives and displacing nearly 4 million of Syria’s 22 million people. There is no sign of a breakthrough for either side, though rebels have scored some recent gains on the battlefield and in the diplomatic arena.
UN diplomats and officials said Thursday that the capture of the 21 peacekeepers will almost certainly lead to a reexamination of security for the UN monitors and their patrols in the field.
The UN mission, known as UNDOF, was set up in 1974, seven years after Israel first captured the Golan and a year after it managed to push back Syrian troops trying to recapture the territory in another regional war.
For nearly four decades, the UN monitors helped enforce a stable truce between Israel and Syria, making it one of the most successful UN missions in the world, said Timor Goksel, a former senior UN official in the region.
The force has an office in Damascus and staffs observation posts along the armistice line. The peacekeepers shuttle between Damascus and the outposts to deliver supplies and rotate crews.
Goksel, who works for the Al-Monitor news website, said the observers are ‘‘soft targets’’ in Syria’s increasingly brutal civil war. Up to now they were ‘‘never challenged by anybody in Syria,’’ he added.
The monitors’ success may have been linked to a decision by Assad and his father and predecessor Hafez Assad to comply with the armistice deal, including limits on military hardware allowed near the cease-fire line.
An Israeli official said that if UNDOF were to halt operations, it would be a ‘‘bad thing for peace.’’ He spoke on condition of anonymity because he was not authorized to discuss the diplomatically sensitive issue with the media.
Israel has said it’s trying to keep out of the Syria conflict but is watching the disintegration of the country with growing concern.