Syrian rebels holding dozens of Fijian UN peacekeepers hostage have attacked Filipino troops in the Golan Heights, Philippine officials said.

Philippine peacekeepers at one UN encampment were attacked, but those at another were "extricated," Defence Secretary Voltaire Gazmin told reporters in a series of text messages, adding that the attack started early on Saturday Syrian time.

Philippine military spokesman Ramon Zagala told reporters, "there is an ongoing firefight, but all Filipinos are safe."

There were 40 Filipino troops in the encampment that came under attack, and 35 in the second, according to the Philippine military.

The Syrian rebels seized 44 Fijian peacekeepers on Thursday.

The rebels then demanded that the 75 Filipinos manning two separate UN encampments 4 km apart surrender their weapons, but they refused.

The situation of the peacekeepers, whose mission monitors a 1974 disengagement accord between Syria and Israel, remains "very, very fluid," the UN secretary-general's spokesman, Stephane Dujarric, told reporters on Friday at the UN headquarters in New York.

The UN said in a statement that it had received assurances from credible sources that the Fijian peacekeepers "are safe and in good health."

The statement added that they had been informed "the intention behind holding the peacekeepers was to remove them from an active battlefield to a safe area for their own protection."

The UN mission, known as UNDOF, has 1,223 troops from six countries: Fiji, India, Ireland, Nepal, Netherlands and the Philippines.

But the Philippine government said last week that it would bring home its 331 peacekeeping forces from the Golan Heights after their tour of duty ends in October, amid deteriorating security in the area.

Various Syrian rebel groups have been engaged in intense fighting with the Syrian military in and near the Golan Heights.