A UN convoy attempting to pick up 21 Filipino peacekeepers that their Syrian rebel captors had agreed to free was forced back by a barrage of army shelling on Friday, a watchdog said.
In New York the United Nations said efforts to secure the peacekeepers would resume on Saturday.
"Arrangements were made with all parties for the release of the 21 peacekeepers," said UN peacekeeping spokeswoman Josephine Guerrero, "but due to the late hour and the darkness it was considered unsafe to continue the operation. Efforts will continue tomorrow."
UN peacekeeping chief Herve Ladsous said the village where the soldiers are being held came under intense shelling.
That was denied by Syrian UN Ambassador Bashar Jaafari, who said everything was being done to get them out safely.
Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, said a UN convoy entered the village of Jamla to collect the peacekeepers but the army shelled the area.
"When the UN vehicles entered into Jamla, the Syrian army shelled a nearby village. The UN cars then withdrew from Jamla," said Abdel Rahman.
Ladsous and expressed hope that a possible ceasefire would lead to the freeing of the peacekeepers, who have been held by Syrian rebels since Wednesday.
"That village is subject to intense shelling by the Syrian armed forces," he said. "There is perhaps a hope, but it is not done yet... that a ceasefire of a few hours can intervene which would allow for our people to be released."
The peacekeepers "have been spread into five or four locations within that village in the basement of various houses."
Jaafari said: "Syrian forces are not targeting the village, they are doing everything in order to bring back safely the peacekeepers and get the armed terrorist groups out of there."
US State Department spokeswoman Victoria Nuland accused the Syrian regime of "making it impossible for UN negotiators to get in there and try to resolve it."
The Filipinos, members of the UN Disengagement Observer Force (UNDOF) monitoring the armistice line between Syria and Israel that followed the 1973 Arab-Israeli war, were abducted just one a mile to the Syrian side of the line.
The rebels are demanding that Syrian troops move 20 kilometres (12 miles) back from Jamla, an area at the southern end of the armistice zone in the Golan, Philippine foreign affairs spokesman Raul Hernandez said.
He said Manila had received information suggesting the 21 peacekeepers would be released on Friday.
"We are trying to intensify our negotiations with the rebel groups," he said adding that the hostages were nonetheless being treated well.
The Observatory said the rebels had added a fresh demand.
"They are now demanding a new condition -- that the International Committee of the Red Cross guarantees the safe exit from the strife-torn area of Jamla of civilians," Abdel Rahman told AFP.
In Manila, the brother of one of hostages issued a televised appeal for the peacekeepers' release.
Xy-son Meneses said he was concerned for his brother, Captain Xy-rus Meneses, who appeared in an Internet video with the other captured Filipinos shortly after their abduction.
"They are not there to cause trouble but to help maintain peace in Syria so I ask if they can release them," he said.
Concern has been mounting that the abduction might prompt more governments to withdraw troops from the already depleted UN mission.
Israeli officials warned that any further reduction in its strength 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 Israeli army revealed that it helped eight UN peacekeepers redeploy through Israeli-held territory overnight from an isolated post in the area where the hostages are being held.
"Eight UNDOF soldiers were evacuated from a post located within the demilitarised zone in the Syrian Golan Heights," an army spokeswoman said, adding that Israeli troops escorted them north to another UN base.
World powers remain at loggerheads over the way forward, with Western governments firm in their demand for President Bashar al-Assad to quit, and China and Russia equally firm in their opposition to any imposed regime change.
"You know that we are not in the regime-change game," Russian Foreign Minister Sergei Lavrov reiterated on Friday. "We are against interference in domestic conflicts," he told the BBC.
On Friday the Syrian army pounded rebel areas in the central city of Homs with warplanes and tanks, the Observatory said, as protesters demonstrated against the army offensive.
A total of 121 people were killed in the Syrian conflict on Friday, the Observatory said.