Syrian armed groups, some of whom are linked to al-Qaeda, captured 43 UN peacekeepers on the Syrian side of the Golan Heights on Thursday and surrounded 81 others, the UN said.
The 43 peacekeepers from Fiji were forced to surrender their weapons and taken hostage near the Quneitra crossing, but 81 Filipino blue helmets "held their ground" and refused to disarm, the Filipino defence department said.
"This resulted in a stand-off which is still the prevailing situation at this time, as UN officials try to peacefully resolve the situation," said the statement from Manila.
Fiji army chief Brigadier-General Mosese Tikoitoga said the captured peacekeepers were all safe, and asked people in the Pacific nation to pray that they are released unharmed.
"(The) men are safe and well even, though they are detained by armed rebels in the Golan region," he told reporters in the capital Suva.
Syrian rebels, including fighters from the Al-Qaeda affiliate Al-Nusra Front, stormed the crossing at Quneitra on Wednesday, sparking an exchange of gunfire with Israeli troops.
Quneitra is the only crossing between the Syrian and the Israeli-controlled side of the strategic plateau.
The UN Security Council "strongly condemned" the detention of the 43 and the "surrounding of positions" manned by the 81 other peacekeepers, by "terrorist groups and by members of non-state armed groups."
The council demanded the "unconditional and immediate release of all the detained United Nations peacekeepers" and urged countries with influence to help win their release.
The 81 Filipino troops were locked in a standoff near Ar Ruwayhinah and Burayqah, while the Fijian soldiers were taken to the southern part of the buffer zone, UN officials said.
UN spokesperson Stephane Dujarric said it was unclear which group had staged the attacks.
"Some groups are self-identified as affiliated to Al-Nusra but we are not able to confirm," he said.
The US State Department pointed the finger at Al-Nusra, however.
"The United States strongly condemns the detention of UN peacekeepers and ongoing violence targeting the UN Disengagement Observer Force (UNDOF) in the Golan Heights by non-state armed groups, including UN Security Council-designated terrorist group Al-Nusra Front," US State Department spokeswoman Jen Psaki said in a statement.
Washington demanded the "unconditional and immediate release" of the blue helmets.
Threats to peacekeepers
UN officials noted that peacekeepers monitoring the armistice line between Israel and Syria were detained twice last year before being released safely.
In June 2013, there was a similar takeover of the crossing by rebel forces, but the Syrian army managed to regain control.
Six countries contribute troops to the 1,200-strong United Nations Disengagement Observer Force (UNDOF): Fiji, India, Ireland, Nepal, the Netherlands and the Philippines.
The Philippines, which has 331 troops serving in UNDOF, announced on Saturday that it will pull out of the peace force, citing security concerns.
Filipino defense officials said no fresh troops would be sent to serve in UNDOF once the current soldiers return from duty in October.
Last year, Manila also considered pulling its Golan peacekeepers out after 25 of them were kidnapped but later freed by Syrian rebels in two separate incidents.
A Filipino soldier was also wounded by a wayward shell last year.
Since the Syrian conflict erupted in 2011, the plateau has been tense, with a growing number of rockets and mortar rounds hitting the Israeli side, mostly stray, prompting occasional armed responses.
During fighting on Wednesday, several mortars landed in or near UN positions.
Israel, which has yet to sign a peace deal with Syria, seized 1,200 square kilometers (460 square miles) of the Golan Heights during the 1967 Six-Day War and later annexed it in a move never recognized by the international community.