Syrian National Coalition, the opposition umbrella group, asked to send representative to Doha summit later this month.
UN peacekeepers held hostage by Syrian rebels while patrolling the sensitive armistice line with Israel have said they are safe and being catered for.
Several videos posted on the Internet on Thursday showed footage of some of the group, with one of the peacekeepers saying they were not in danger.
The 21 Filipinos were detained on Wednesday at a rebel post and have entered a second day in detention despite a chorus of international condemnation and calls for their release.
The detention occurred just one and a half kilometres on the Syrian side of the armistice line at its southern end towards the Yarmouk River on the border with Jordan.
The rebels, calling themselves the Yarmouk Martyrs Brigade, demanded in video statements that Syria withdraw its troops from Jamla and neighbouring villages in the area.
Diplomats scrambled to secure the peacekeepers’ release as concern mounted that their seizure might prompt more governments to withdraw their contingents from the already depleted UN mission.
Israeli officials warned that any further reduction in the strength of the UN Disengagement Observer Force (UNDOF) risked creating a security vacuum in the no-man’s land between the two sides on the strategic Golan Heights.
One of Thursday’s videos, shows three men dressed in camouflage and blue bullet-proof vests emblazoned with the UN and “Philippines.”
“We, the UN personnel here, are safe, and the Free Syrian Army are treating us good,” one of them says in English.
“We cannot go home because the government of (President Bashar) Assad do not stop the bombing. To our family, we hope to see you soon and we are OK here.”
The second video shows six peacekeepers sitting in a room. An officer, who identifies himself as a captain, says that as their convoy came under shelling on Wednesday, “we stopped and civilian people helped us for our safety and distributed us in different places to keep us safe.”
A spokesman for the Martyrs of Yarmouk Brigades, which is holding the peacekeepers, told The Associated Press via Skype that all the 21 peacekeepers “are fine and in good health.”
“We consider them guests,” he added.
The Philippines strongly condemned the seizure of its troops and demanded they be released immediately, a call echoed by Ban Ki-moon, the UN chief.
Philippine President Benigno Aquino said he had received assurances the peacekeepers would not be harmed.
“I understand they are being treated well….so far, nobody has been saying that they are in danger,” Aquino told reporters.
Vitaly Churkin, Russia’s UN ambassador and the current Security Council president, said talks were under way between UN officials from the peacekeeping force and the captors.
Churkin said the capture of the peacekeepers “is particularly unacceptable and bizarre” because the UNDOF peacekeepers are unarmed and their mission has nothing to do with Syria’s internal conflict.
“They are there on a completely different mission, so there is no reason at all under any circumstances, any kind of sick imagination to try to harm those people,” he said.
The captive troops are part of a 300-strong Philippine contingent to a UNDOP force that has been monitoring the separation of Israeli and Syrian troops since the 1974 armistice that followed the previous year’s Middle East war.
At the end of February, UNDOF comprised some 1,000 peacekeepers but a growing number of incidents over the past year has made it increasingly difficult for the United Nations to keep the mission up to strength.
Canada and Japan had already withdrawn their small contingents and Croatia announced last week it was pulling out its 100 troops.
The Philippine president said no decision had yet been made on the future of Manila’s contingent but its withdrawal would leave just Austrian and Indian troops.
In video statements on Wednesday, a rebel spokesman said the peacekeepers would not be freed until Syrian government forces pull out of the area.
“If they do not withdraw, these men will be treated as prisoners,” spokesman Abu Kaid al-Faleh said, accusing the UN force of working with the Syrian army against the rebels.
Meanwhile, the Iraqi government closed the Yaarubiyeh border crossing with eastern Syria and sent in military reinforcements after cross-border fire killed an Iraqi soldier.
Nationwide violence claimed 179 lives on Wednesday, 73 rebels, 57 civilians and 49 soldiers, it added.
The United Nations says that more than 70,000 people have been killed and more than one million fled the country since the revolt against President Bashar al-Assad’s rule erupted in March 2011.