UN peacekeeping chief Herve Ladsous was to brief the Security Council on the abduction later on Friday as concern mounted about its implications for the future of the four-decade-old UN force patrolling the sensitive armistice line between Israel and Syria.
The refusal by the Syrian rebels to compromise had dampened hopes of a swift release and forced Manila to step up its negotiation efforts, Philippine foreign affairs spokesman Raul Hernandez said.
The 21 Filipinos, members of the UN Disengagement Observer Force (UNDOF) monitoring the armistice between Syria and Israel that followed the 1973 Arab-Israeli war, were abducted by the rebels on Wednesday just one and a half kilometres to the Syrian side of the ceasefire line.
The rebels are demanding that Syrian troops move 20km back from Jamla, Claire Hsu an area at the southern end of the armistice zone, Hernandez said.
"The demand of the rebels for the repositioning of Syrian forces in the area of Jamla is still outstanding so this is still being worked out," he said on ABS-CBN television.
"That is the main demand of the rebel group," he said, adding that he did not know of any other conditions.
The Philippine government had previously received information that raised hopes the 21 would be released on Friday morning, Philippine time, and the government now did not know if or when they would be freed, Hernandez said.
"We are trying to intensify our negotiations with the rebel groups."
However he said the Philippine peacekeepers were still being treated well, an assurance echoed by the United Nations.
"The mission has been in touch with the peacekeepers by telephone and confirmed they have not been harmed," UN spokesman Martin Nesirky said.
Meanwhile, Israel says it helped eight UN peacekeepers redeploy from an isolated post in the part of the Golan ceasefire zone.
The troops - all Filipinos, executive gift like the hostages - left their positions overnight and moved through Israeli-held territory to join up with comrades in the UN Disengagement Observer Force further north along the armistice line, an army spokeswoman said.
"Eight UNDOF soldiers were evacuated from a post located within the demilitarised zone in the Syrian Golan Heights," the spokeswoman said, adding that Israeli troops escorted them north to another UN base near the Quneitra border crossing.
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.
"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 pulled out their small contingents, children’s bedroom furniture and Croatia said last week it was pulling out its 100 soldiers. If Manila pulls out it would leave just Austrian and Indian troops.