Twenty-one United Nations peacekeepers held by rebels for three days in southern Syria have crossed into Jordan.

The Filipino peacekeepers were seized by the Martyrs of Yarmouk rebel brigade on Wednesday.

They are part of the UN Disengagement Observer Force (UNDOF) that has been monitoring a ceasefire line between Syria and Israel in the Golan Heights since 1974.

They were taken by the rebels on Saturday to the Jordanian border, about 10km south of the village of Jamla where they had been held since being captured.

In the Syrian capital, Mokhtar Lamani, who heads the Damascus office of UN-Arab League mediator Lakhdar Brahimi, confirmed that the men had crossed into Jordan.

Jordan appeared surprised by the arrival of the peacekeepers - who had been expected to be retrieved instead by a UN convoy inside Syria and possibly taken to Damascus.

Syria expressed dismay at how they were spirited across the border.

The move would "encourage terrorists to repeat these events", the foreign ministry in Damascus said, adding that Syria had complied fully with its commitment to ensure the peacekeepers' safety.

UN Secretary-General Ban Ki-moon welcomed the release of the peacekeepers but called on "all parties to respect UNDOF's freedom of movement and the safety and security of its personnel", Mr Ban's spokesman said.

A brief truce was agreed this morning to allow for the peacekeepers' retrieval.

Although the two-hour window of that ceasefire passed before they could be extracted, the relative calm prevailed long enough for the rebels to take them south to Jordan, rebels said.

A rescue effort last night was delayed by heavy bombardment and abandoned after nightfall, UN peacekeeping chief Herve Ladsous said.