Israeli soldiers walk past an unmanned U.N. watchtower May 7, 2013, on the Israeli side of the border between Golan Heights and Syria. Four U.N. peacekeepers were seized in demilitarized area. (Uriel Sinai/GETTY IMAGES)

Syrian rebels kidnapped four United Nations peacekeepers Tuesday along the fraught cease-fire line between Israel and Syria in the Golan Heights, in a replay of a similar incident in March.

The U.N. peacekeeping department in New York said four Philippine peacekeepers serving in the U.N. Disengagement Observer Force were captured by “an unidentified armed group” while patrolling near the town of Jamlah.

“All efforts are currently underway to secure their release,” said Kieran Dwyer, a spokesman for the Department of Peacekeeping Operations.

In a statement posted on Facebook, the rebel Yarmouk Martyrs Brigade announced that it seized the peacekeepers to “secure and protect” them from heavy shelling by Syrian government forces. The statement was accompanied by a photograph of the peacekeepers sitting barefoot on a carpet and wearing light-blue U.N. armored vests, three of which were marked “Philippines,” over their camouflage fatigues.

The Yarmouk Martyrs Brigade abducted 21 Philippine peacekeepers in the same area in March. The group first claimed it was holding those U.N. observers as leverage to compel the Syrian government to withdraw its forces from Jamlah, where the troops had clashed with rebels. But after intensive negotiations between the United Nations and the rebels, the group released the peacekeepers along the Jordanian border, saying it had detained them for their own safety.

The Yarmouk Martyrs Brigade said the four observers were taken Tuesday after government forces captured a checkpoint near the area they were patrolling, “which endangered their lives, pushing us to intervene.”

The statement also described “heavy clashes and heavy shelling” in the area, suggesting that the rebels may have seized the peacekeepers in part to protect themselves. It said the peacekeepers were endangered not only by “members of the regime army” but by “some criminal groups” as well.

In New York, U.N. Secretary General Ban Ki-moon condemned the detention and called for the peacekeepers’ immediate release. He urged all parties to respect the “freedom of movement and safety and security” of the U.N. Disengagement Observer Force.

Unarmed members of the observer force have patrolled the no man’s land between Syria and Israel since 1974 , monitoring a cease-fire between the two countries following the October 1973 Arab-Israeli war. Israel occupied most of the Syrian Golan Heights during the Six-Day War in 1967. The peacekeepers have continued their patrols even as fighting between Syrian rebels and forces loyal to President Bashar al-Assad has spread into the area, bringing shellfire and clashes to the zone under U.N. supervision.

The abduction took place in the rugged no man’s land, where shepherds still move flocks down deep canyons and dry riverbeds, in a triangle of land that borders Syria, Jordan and the Israeli-occupied Golan Heights.

While the mosques still call people to prayer, the towns are very quiet, and few vehicles appear on the road. Some of the houses are damaged by mortars or shelling.

From an Israeli military observation post, one can see an old Ottoman-era bridge, a Jordanian military and customs depot, and further in the distance, a string of small villages that have changed hands repeatedly in the past year, between regular Syrian army troops and rebel combatants.

Israeli military commanders call the zone an “ungoverned area,” and the Israel Defense Forces have moved tanks and intelligence and combat units to their side of the contested boundary in the Golan Heights.

“This area is no longer stable,” Brig. Gen. Gal Hirsch said in a tour of the area with journalists on Thursday. “Many players are involved now.”

Hirsch pointed to a U.N. post in the hazy distance that was attacked by Syrian artillery a few months ago. “Radicals are building their future infrastructure right here. Places like this are heaven for terrorists.”

Booth reported from Jerusalem. Ruth Eglash in Jerusalem, Ahmed Ramadan in Beirut and Colum Lynch at the United Nations contributed to this report.