Syrian rebels on Wednesday abducted more than 20 UN peacekeepers in the Golan Heights ceasefire zone pushing back the frontier of their war with President Bashar al-Assad.
The United Nations said it is trying to negotiate the release of the Philippines soldiers. But a spokesman for the rebels said in a video that the UN troops would be held until Assad's forces pull back from a village in the Golan.
About 30 armed fighters stopped a UN Disengagement Force (UNDOF) convoy in the ceasefire zone, where the UN has had peacekeepers monitoring a ceasefire between Syria and Israel since 1974, UN deputy spokesman Eduardo del Buey told reporters.
"The UN observers were on a regular supply mission and were stopped near Observation Post 58, which had sustained damage and was evacuated this past weekend following heavy combat in close proximity, at Al Jamlah," he added.
There has been fierce fighting around Jamlah village, which is held by opposition forces.
The UN Security Council released a statement which said "armed elements of the Syrian opposition" had abducted the group of more than 20 peacekeepers and demanded their "unconditional and immediate" release.
"Negotiations are going on and the matter is mobilizing all our teams," UN peacekeeping chief Herve Ladsous told reporters after briefing the Security Council on the abduction. "It is a very serious incident."
Russia's UN ambassador Vitaly Churkin, who read the Security Council statement, said the rebels have made demands directed at the Syrian government but did not give details. "We hope they are going be released immediately," Churkin told reporters.
Syrian rebels are also believed to be holding an UNDOF staffer who was seized last month. The staffer is from Canada, according to diplomats.
UN diplomats and the Syrian Observatory for Human Rights director Rami Abdel Rahman said the peacekeepers were from the Philippines.
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Rahman released two videos in which a rebel group, the Yarmuk Martyrs Brigade, set out their demands for the release of the peacekeepers.
In one, a man identified as Abu Kaid al-Faleh, a spokesman for the brigade, said the peacekeepers would not be freed until Syrian government forces pull back from the area.
"We call on them to withdraw all their troops to their bases. If they do not withdraw, these men (UN troops) will be treated as prisoners," he said.
In a second video, the same spokesman accused the UNDOF of working with the army to try to suppress the insurgency and help regime forces enter Jamlah.
"The Syrian regime, the UN and the European countries are all collaborators with Israel," he said.
The United Nations has reported a growing number of incidents in the Golan zone over the past year. It has already reinforced security for the peacekeepers by sending extra armored vehicles and communications equipment.
Shells from the Syrian side have landed in the ceasefire zone and on Israeli territory. Syrian government tanks have entered the zone several times, according to the UN.
Up to the end of February there were about 1,000 troops from Austria, Croatia, India and the Philippines operating in the ceasefire force.
But Croatia announced last week that it is withdrawing its 100 troops from UNDOF. The Croatian government said it feared for the soldiers' safety after reports that Saudi Arabia had bought arms from Croatia and then provided them to the Syrian rebels.
Canada and Japan have also withdrawn their small contingents in recent months because of security fears.