Armed fighters on Wednesday detained about 20 UN peacekeepers in the Golan Heights between Syria and Israel, a UN spokesman said.
Syrian Observatory for Human Rights director Rami Abdel Rahman said the peacekeepers were from the Philippines.
But the United Nations did not give the nationalities of the UN Disengagement Force (UNDOF) troops taken in the latest incident in the tense Golan zone.
UN deputy spokesman Eduardo del Buey told reporters the UN force had "reported that earlier today approximately 30 armed fighters stopped and detained about 20 peacekeepers within the area of limitation."
"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.
"The mission is dispatching a team to assess the situation and attempt a resolution," the spokesman said.
The United Nations has reported a growing number of incidents in the Golan zone, where it has had peacekeepers since 1974 observing a truce accord between Syria and Israel.
The Britain-based Observatory distributed two amateur videos that carried statements by the rebel Yarmuk Martyrs Brigade claiming the peacekeepers' capture.
In one, a man identified as Abu Kaid al-Faleh, a spokesman for the brigade, said the peacekeepers would not be freed until Syrian regime forces pull out 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 rebel accused the UNDOF of working with the army to try to suppress the insurgency and help regime forces enter Jamla.
"The Syrian regime, the UN and the European countries are all collaborators with Israel," he said.
"They all want the (rebel) Free Syrian Army to leave this land. They want us to leave our land and they want the oppressor Bashar al-Assad to enter because they are collaborators with the Zionists, Israel and America."