Forty-three UN peacekeepers are being held by an "armed group" in the Syrian Golan Heights, a UN spokesperson says.
The UN Disengagement Observer Force (Undof) personnel, from Fiji, were detained near Quneitra, during fighting between rebels and government forces.
Another 81 Filipino peacekeepers are being restricted to their positions near al-Ruwayhina and Burayqa.
It comes a day after rebels took control of a crossing into the Israeli-occupied Golan after a long battle.
Activists said the rebels included members of the al-Nusra Front, al-Qaeda's affiliate in Syria.
During the fighting, an Israeli soldier and an Israeli civilian were wounded by stray bullets. The Israeli military said it had responded with artillery fire at two Syrian army positions.
Mortars also struck near Undof positions, but there were no casualties.
'Area of separation'
The UN spokesperson said the 43 peacekeepers were detained "during a period of increased fighting beginning yesterday between armed elements and Syrian Arab Armed Forces within the area of separation".
"The United Nations is making every effort to secure the release of the detained peacekeepers, and to restore the full freedom of movement of the force throughout its area of operation."
The spokesperson did not specify which armed group was holding them.
This is not the first time Undof personnel have been detained by rebel fighters in recent years. Peacekeepers were detained in March and May of 2013 and were released safely.
The Golan Heights, a rocky plateau in south-western Syria, has a political and strategic significance that belies its size.
Israel seized the region in the closing stages of the 1967 Six-Day War, and thwarted a Syrian attempt to retake it in 1973.
Both countries signed an armistice in 1974, after which Undof was put in place to monitor the demilitarised zone.
It has 1,224 lightly-armed military personnel from Fiji, India, Ireland, Nepal, the Netherlands and the Philippines.