The United Nations said Thursday that 43 peacekeepers serving along the cease-fire line between Syria and Israel have been detained by Syrian rebels during intense fighting in the area between opposition and government forces.

The abductions came a day after rebels claimed control of the border crossing between Israel and Syria amid a sharp escalation of violence in the area. Government warplanes struck rebel positions around the crossing on Thursday, activists and rebels said, as forces loyal to President Bashar al-Assad sought to reclaim the remote crossing.

A U.N. statement said that the peacekeepers were detained Thursday morning and that an additional 81 peacekeepers were trapped by the fighting in two areas of the Golan Heights, most of which has been occupied by Israel since the 1967 Arab-Israeli war.

The 43 detained were Fijians, the statement said, but it gave no details about the nationalities of the other 81 peacekeepers. The Associated Press reported that the 81 were from the Philippines, citing Stephane Dujarric, a spokesman for the U.N. secretary general.

The United Nations gave no further details, but an Israeli military spokesman told CNN that the captors are suspected to be members of al-Qaeda-affiliated Jabhat al-Nusra, which has been fighting alongside more-moderate, Western-backed rebels for control of the area.

The peacekeepers serve with the U.N. Disengagement Observer Force, which has monitored the cease-fire line for 40 years.

Syrian rebels have abducted peacekeepers in the area on two occasions in 2013. In each case, U.N. officials successfully negotiated their release.

The United Nations is making “every effort” to secure the release of the peacemakers and to “restore the full movement of the Force throughout its area of operation,” it said in its statement.