Rebels holding 21 U.N. peacekeepers near the Golan Heights in southern Syria say government forces must leave the area before they free their "guests", an activist in touch with the fighters said on Thursday.
Rami Abdelrahman of the Syrian Observatory for Human Rights quoted a spokesman for the "Martyrs of Yarmouk" rebel brigade as saying the peacekeepers were being held as "guests" in the village of Jamla, about a mile from a ceasefire line with the Israeli-occupied Golan Heights.
"He said they will not be harmed. But the rebels want the Syrian army and tanks to pull back from the area," Abdelrahman said after speaking to the rebel spokesman on Thursday morning.
The capture of the U.N. peacekeepers close to Israeli-held territory was another sign that Syria's conflict, nearing its second anniversary, could spill over to neighboring countries.
Israel has said it will not "stand idle" if violence spreads to the Golan, which it captured in the 1967 Middle East war. But a senior Defense Ministry official voiced confidence on Thursday that the United Nations could secure the peacekeepers' release, signaling that Israel would not intervene.
Suspected Sunni Muslim insurgents killed 48 Syrian troops inside Iraq on Monday and cross-border artillery fired from Syria has killed people in Lebanon and Turkey in recent months.
Wednesday's detention of the peacekeepers by around 30 gunmen will also reinforce Western concerns that any weapons supplied to rebels fighting to overthrow President Bashar al-Assad could end up being turned against Western interests.
Peter Bouckaert of Human Rights Watch said rebels from the Martyrs of Yarmouk have been seen in other videos carrying a grenade launcher that appears to be Croatian. Media reports last month quoted U.S. officials saying Saudi Arabia was sending Croatian arms to Syrian rebels.
The United Nations says around 70,000 people have been killed in the uprising which erupted in March 2011 with mainly peaceful protests against Assad and has spiraled into an increasingly sectarian conflict.
The Philippine government condemned the capture of the peacekeepers - three officers and 18 enlisted men - which it called a "gross violation of international law".
President Benigno Aquino told reporters the peacekeepers were being well treated and that the United Nations was in touch with the rebels to ensure their safety. "By tomorrow they expect all of these 21 to be released," he said, adding their release might occur as early as Thursday.
Aquino said both sides in the Syrian conflict considered the United Nations a "benign presence" in the country - a view not shared by many Syrian rebels, who hold the organization at least partly responsible for a lack of international support.
RIGHTS GROUP INVESTIGATING CLAIMS
In a video released to announce the capture of the U.N. convoy on Wednesday, a member of the Yarmouk Martyrs' Brigade accused the peacekeepers of collaborating with Assad's forces to try to push them out of village of Jamla which the rebels seized on Sunday after heavy fighting.
A Facebook statement issued later in the name of the Yarmouk Martyrs denied the U.N. soldiers had been detained and said they were being protected from bombardment by Assad's forces.
That statement appeared at odds not only with the original rebel statement but with the footage showing the convoy halted in the middle of a road, with U.N. personnel stuck inside their vehicles, exposed to any artillery shells that might fall.
Human Rights Watch said it was investigating the Yarmouk Martyrs for involvement in past executions, including a videotaped killing of Syrian soldiers which was posted on the Internet on Tuesday.
One video showed rebels with several men in army fatigues they said were captured at a Syrian army base near Jamla. Another video showed 10 dead men, including some of the captives filmed alive in the earlier video.
Peacekeepers of the U.N. Disengagement Observer Force (UNDOF) mission have been monitoring a ceasefire line between Syria and the Israeli-occupied Golan Heights for four decades.
The U.N. Security Council and Secretary-General Ban Ki-moon condemned the seizure of the observers and demanded their immediate release.
"The U.N. observers were on a regular supply mission and were stopped near Observation Post 58, which had sustained damage and was evacuated this past weekend following heavy combat in close proximity at Al Jamla," the United Nations said, referring to a village which saw fierce clashes on Sunday.
It said the peacekeepers were taken by around 30 fighters.
In one rebel video, a young man saying he was from the Martyrs of Yarmouk brigade stood surrounded by several rebel fighters with assault rifles in front of two white armored vehicles and a truck with "UN" markings.
"The command of the Martyrs of Yarmouk ... is holding forces of the United Nations Disengagement Observer Force until the withdrawal of forces of the regime of Bashar al-Assad from the outskirts of the village of Jamla," he said.
At least five people could be seen sitting in the vehicles wearing light blue U.N. helmets and bulletproof vests. "If no withdrawal is made within 24 hours we will treat them as prisoners," the man said.
Syria announced on Thursday it had uncovered an Israeli spy camera monitoring a "sensitive site" on its Mediterranean coast, saying the discovery highlighted Israel's role in the uprising and insurgency against Assad. Israeli officials made no comment on the Syria report.
Additional reporting by Oliver Holmes in Beirut, Manuel Mogato in Manila and Jeffrey Heller in Jerusalem; Editing by Jon Hemming