Seventy-five Filipino members of a UN peacekeeping force besieged by Syrian rebels on the Golan Heights are ready to use "deadly force" to defend themselves, their commander in Manila said on Friday.

Talks were under way to free a separate group of 43 peacekeepers from Fiji who were taken hostage by the anti-Damascus fighters, officials said.

The United Nations Security Council "strongly condemned" the assaults against the peacekeepers, which it said were carried out by "terrorist groups and by members of nonstate armed groups".

The Filipino peacekeepers trapped at two posts on the Syrian side of the Golan Heights were prepared to fight back rather than surrender, their commander in Manila said.

"We can use deadly force in defense of the UN facilities," Colonel Roberto Ancan told reporters.

"I (would) just like to emphasize our troops are well-armed, they are well-trained ... they are well-disciplined warrior peacekeepers."

Syrian rebels, including fighters from the al-Qaeda affiliate al-Nusra Front, stormed a Golan Heights crossing on Wednesday, sparking an exchange of gunfire with Israeli troops.

The rebels then captured 43 Fijian members of the UN Disengagement Observer Force on the Syrian side on Thursday, forcing them to surrender their weapons and taking them hostage.

Ancan said the rebels used an English-speaking Fijian hostage to relay their demand to the Filipino peacekeepers to give up their weapons, but they refused.

Meanwhile, talks were under way to release the Fijian hostages, according to the Pacific nation's Prime Minister Voreqe Bainimarama, who said they were believed to be safe.

"I want to assure the families of the soldiers we are doing everything possible to secure their safe return," Bainimarama said in a statement.

"The latest information we have is that they are safe, and I can say now that the negotiations for their release have already begun."

Manila called for the "immediate release" of the Fijian troops and the "immediate withdrawal of all non-UN forces around UNDOF positions," foreign affairs spokesman Charles Jose said.