The threat underscored the widening risk that the Syria conflict is destabilizing the Middle East, and raised new concerns about the agendas of some Syrian insurgent groups, just as Western nations, including the United States, were grappling over whether to arm them.

The seizure of the peacekeepers was the second serious war-related Syria border problem this week. On Monday, more than 40 Syrian soldiers who had sought temporary safety in Iraq were killed in an ambush as the Iraqi military was transporting them back to the Syrian border. At the United Nations, Eduardo del Buey, a spokesman for Secretary General Ban Ki-moon, suggested that officials had long feared the possibility of harm to the peacekeepers. “As the secretary general has said repeatedly, the spillover effects of the Syrian crisis pose a danger to the region as a whole and to the countries and the areas in the neighboring states around it, and Undof is no exception,” he said, using the acronym for the Golan peacekeeping mission. “They are in a zone where the spillover could be of consequence.”

Ambassador Vitaly I. Churkin of Russia, which holds the monthly presidency of the Security Council for March, said that members had been briefed about the Golan situation but that he could provide no further information on what precisely had happened. Mr. Churkin, whose government is a main supporter of the Syrian government in the conflict and a strong critic of the armed rebels, urged the captors to release the peacekeepers immediately. “They should stop this very dangerous course of action,” he told reporters.

Linking the Golan situation to the Iraq killings two days earlier, Mr. Churkin said: “Some people are trying very hard to extend the Syrian conflict. Today there is this incident. This is no man’s land between Syria and Israel. Somebody is trying very hard to blow this crisis up.”

With a force of 1,011 troops contributed by Austria, Croatia, India and the Philippines, the United Nations observer force in the Golan is responsible for maintaining the fragile calm between Israeli and Syrian troops at the demilitarized zone along Syria’s Golan frontier, established after a cease-fire ended the 1973 Arab-Israeli war.

Image Credit... The New York Times

The detention of the peacekeepers came less than a week after Croatia announced it was withdrawing its soldiers from the Golan force, following reports that Croatia was selling weapons funneled to Syrian rebels by Saudi Arabia, a main supporter of the insurgency. The Croatian government denied the reports but said they had put the safety of its peacekeepers at risk. It is unclear which country or countries will replace the departing Croatians.