The UN pressed on with negotiations on Thursday to secure the release of 21 peacekeepers abducted in Syria as regime warplanes pounded the northern city of Raqa after it fell into rebel hands.

A video posted on the Internet showed footage of six members of the group of Filipino peacekeepers, who were patrolling the sensitive armistice line with Israel, when they were seized on Wednesday by Syrian rebels. One of them said they were safe and being cared for, and the UN confirmed they had not been harmed.

“The mission has been in touch with the peacekeepers by telephone and confirmed they have not been harmed,” UN spokesman Martin Nesirky said in New York. A UN official said the UN Disengagement Observer Force mission was “negotiating with the armed group and the Syrian authorities” to obtain a release. Concern has been mounting that their seizure might prompt more governments to withdraw their contingents from the already depleted UN mission.

Israeli officials warned that any further reduction in the strength of UNDOF risked creating a security vacuum in the no-man’s land between the two sides on the strategic Golan Heights, which it seized in the 1967 Six-Day War.

The peacekeepers were detained at a rebel post just one and a half kilometres (a mile) on the Syrian side of the armistice line at its southern end towards the Yarmuk River on the border with Jordan. The rebels, calling themselves the Yarmuk Martyrs Brigade, demanded in video statements that Damascus withdraw its troops from Jamla and neighbouring villages in the area. “If they do not withdraw, these men will be treated as prisoners,” spokesman Abu Kaid al-Faleh said, accusing the UN force of working with the Syrian army.

Manila condemned the seizure of its troops and demanded they be released immediately, a call echoed by UN chief Ban Ki-moon. Philippine President Benigno Aquino said he had received assurances the peacekeepers would not be harmed. “I understand they are being treated well... so far, nobody has been saying that they are in danger,” Aquino said.

The peacekeepers are part of a 300-strong Philippine contingent that has been monitoring the separation of Israeli and Syrian troops since the 1974 armistice that followed 1973 Arab-Israeli war. Israel, which annexed the Golan Heights in 1981 in a move never recognised by the international community, said it feared any depletion of the UN force would pose a serious threat. “This kidnapping is likely to convince countries who participate in this force to bring their troops home, which would undoubtedly create a dangerous vacuum in no-man’s land on the Golan,” an Israeli official said.

Canada and Japan have already withdrawn their small contingents and Croatia said last week it was pulling out its 100 troops. If Manila pulls out it would leave just Austrian and Indian troops.

Syrian State television on Thursday broadcast pictures of “Israeli spy gear” unearthed in Syria, in what it said was proof of Israel’s involvement in the armed revolt against President Bashar al-Assad. The broadcaster showed footage of rocks used to “camouflage” surveillance cameras found on the Syrian coast, as well as recording and video devices to transmit pictures and audio “in real time” from “sensitive locations”. “This is proof of Israel’s role in events in Syria,” an unidentified officer said in the broadcast.

Meanwhile, violence across Syria on Thursday killed 123 people, the Britain-based Observatory said. It also reported that fighter jets pounded the northeastern city of Raqa in a bid to recapture it.

Opposition National Coalition chief Ahmed Moaz al-Khatib sent letters to the UN, Arab League and Islamic Conference Organisation chiefs warning that the “blood of the Syrian people will be a curse for the whole world” unless it acts to stop the bloodshed. The UN says more than 70,000 people have been killed in Syrian over nearly two years of conflict, millions have been displaced and more than one million fled the country. Meanwhile, Syria’s ruling Baath Party issued a statement to mark its 50th anniversary on Friday saying the regime will overcome the crisis and “emerge from it stronger.”

Germany’s foreign minister warned on Thursday that delivering weapons to Syria’s rebels could result in an arms race in the region and stressed the EU would send only “defensive” equipment. In an interview with the Tagesspiegel daily, Guido Westerwelle said the situation in Syria was “shocking” and said Berlin would do everything it could to contribute to a political solution “despite all the difficulties.” But he cautioned against arming rebels attempting to topple President Bashar al-Assad, after the chief of staff of the rebel Free Syrian Army said they could bring down the regime “in a month” with the right weaponry.

President Bashar al-Assad on Thursday hailed Turkish opposition to Prime Minister Recep Tayyip Erdogan’s backing for the revolt that began in Syria nearly two years ago, in a statement seen by AFP.The statement comes after Assad met a Turkish opposition delegation, which prompted Erdogan to issue a stinging criticism of the politicians, asking why they were meeting with “such a dictator.”

Assad told the Republican People’s Party delegation there was “a need to distinguish between the stance of the Turkish people, who support stability in Syria, and the positions of Erdogan’s government, which supports terrorism, extremism and destabilisation in the region,” it said.

“The Syrian people appreciates the position adopted by forces and parties in Turkey that reject the Erdogan government’s negative impact on our societies, which are multi-religious and multi-ethnic,” Assad said.The Turkish delegation, headed by Hassan Akgul, stressed “the Turkish people’s refusal to interfere in Syrian affairs, and a commitment to good neighbourly relations,” the statement said.