Syrian rebels on Sunday released four Filipino U.N. peacekeepers they abducted last week, a military spokesman in the Philippines said.

The four, seized Tuesday, were apparently unharmed, but will undergo a medical checkup and stress debriefing, said Brig. Gen. Domingo Tutaan.

The peacekeepers are part of a U.N. contingent that patrols a buffer zone between Syria and the Israeli-controlled Golan Heights, a plateau Israel captured from Syria in 1967.

It was the second abduction of Filipino peacekeepers since March, when 21 were held for three days by rebels fighting the regime of Syrian President Bashar Assad.

The Philippine foreign secretary has said he would recommend withdrawing Filipinos from the peacekeeping contingent in Syria, but the final decision is up to the country's president.

Nearly 1,000 U.N. peacekeepers are patrolling the Golan Heights. Other major contributors are India and Austria. Croatia has recently withdrawn its contingent.

The buffer zone between Syria and the Israeli-controlled Golan had been largely quiet for four decades, but tensions have risen there since the outbreak of the revolt against Assad more than two years ago.

The uprising escalated into a civil war that has claimed tens of thousands of lives and displaced millions of Syrians. The two sides have been largely deadlocked on the battlefield.

Also Sunday, six mortar shells struck a neighborhood in the Syrian capital, Damascus, causing damage and casualties, a Syrian official said on condition of anonymity because he is not authorized to brief reporters.

The mortars hit the predominantly Alawite district of Mazzeh 86 during morning rush hour, he said. Sunday is the first day of the work week in Syria.

Alawites, including Assad, are followers of an offshoot of Shiite Islam, and have dominated government under Assad family rule. Rebels and regime forces have been fighting in parts of Damascus, and have fired mortars at neighborhoods seen as pro-Assad.

The Britain-based Syrian Observatory for Human Rights, an activist group, confirmed that mortars struck Mazzeh 86, but said it had no immediate reports of casualties.