The refusal by the Syrian rebels to compromise had dampened hopes of the UN peacekeepers being released quickly, and forced the government to step up its negotiation efforts, foreign affairs spokesman Raul Hernandez said.
"The demand of the rebels for the re-positioning of Syrian forces in the area of Jamla is still outstanding so this is still being worked out," he said on ABS-CBN television.
The rebels want the Syrian troops to move 20 kilometres back from Jamla, an area in the Golan's ceasefire zone, before they will free the Filipinos, he said.
"That is the main demand of the rebel group," he told AFP, adding 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," he said.
However he said the Filipino peacekeepers were still being treated well.
"(They are) being treated as guests and are unharmed," Hernandez said.
The 21 Filipino troops, members of the UN Disengagement Observer Force (UNDOF) observing a 1974 ceasefire between Syria and Israel, were abducted on Wednesday by the rebels.
A UN official, speaking on condition of anonymity, previously said the UNDOF mission was "negotiating with the armed group and the Syrian authorities" to obtain a release.
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