UN officials shuttled along the rocky frontier between Syria and the Golan Heights on Friday, trying to establish the whereabouts of 43 United Nations peacekeepers seized by Al-Qaida-linked militants inside Syria.Israeli forces took up positions at Quneitra, a fortified crossing between Syria and the Golan, barely 400 meters from Nusra Front militants, who attacked a UN base on the Syrian side of the border on Wednesday and seized the 43 Fijians.About 80 UN soldiers from the Philippines, all of whom serve with UNDOF, a UN force that has monitored the disengagement zone between Israel and Syria since the 1973 Arab-Israeli War, remain locked down in two camps on the Syrian side of the frontier, military officers in the Philippines said.Officials from UNDOF, which has about 1,200 peacekeepers from six countries operating in the zone, declined to comment as they left one of their compounds on Friday.Israeli soldiers, including some redeployed from Gaza, prevented anyone moving too close to the border."We're not doing anything, we're just watching," said an Israeli officer, his platoon hunkered down behind a mound of rocks a few hundred yards back from the crossing, the blue UN flag fluttering above the compound in the near distance.From a lookout point on the Israeli-controlled side, with views across southeastern Syria, Nusra Front rebels could be seen moving on motorbikes and in pick-up trucks, while further away the Syrian army battled opposition forces.The sound of shelling and heavy gunfire echoed across the valley and plumes of smoke rose from buildings as the fighting played out barely two km (1.2 miles) away.It is the third time in two years that UNDOF troops have been seized on the Syrian side of the demarcation zone, a measure of the instability since the uprising against Syrian President Bashar Assad began. Until then, UNDOF had been one of the quietest UN peacekeeping posts anywhere in the world.In both previous cases those seized were released within days, UN officials said. But the situation appears to be more precarious this time. A militant close to the Nusra Front said the Fijians had been taken because they had been providing medical treatment to wounded soldiers from Assad's army.In Manila, a senior officer said the Filipino troops holed up on the Syrian side were well-armed, well-trained and had no intention of surrendering to the rebels."Our position is a well-fortified position in the area of separation," said Colonel Roberto Ancan, commander of the Philippines Peacekeeping Mission Operation Center.The Nusra Front had used a Fijian to urge the Filipinos to surrender, he said, but they would not."This is just part of the job and they are committed to the mission at hand," Ancan said.The Golan is a strategic plateau captured by Israel in the Six-Day War and Syria and Israel technically remain at war. UNDOF monitors the area of separation, a narrow strip of land running about 45 miles (70 km) from Mount Hermon on the Lebanese border to the Yarmouk River frontier with Jordan.A high, rocky plain dotted with mountain peaks and scattered with fruit farms and vineyards, it is also a popular destination for Israelis and foreign tourists.The fighting did not appear to deter them.In slightly surreal scenes, tour groups gathered to watch the battle unfold from a viewing point, including a busload of German visitors and a group of Orthodox Jews."I feel safer here than I would do in San Francisco," said David Schneider, 62, a New Yorker who moved to Israel 30 years ago, watching the rebels through a pair of binoculars.Another local, a former Israeli soldier who fought against Syria in the 1967 war, when the Golan Heights were seized, and then again in 1973, called out the types of weapons being used, identifying them by their sound."That's a Russian-made .50 caliber gun," he said as a heavy 'ratatat' thudded across the plain. "The Syrian army has those."Israeli civilians employed by UNDOF were told not to enter the base on the Israeli side on Friday, amid fears of attack from across the demarcation line. They too gathered on a high hill looking into Syria to observe developments.One employee, Arab-Israeli mechanic Adel Basha, said he had been in the UNDOF compound on Wednesday when the Nusra Front militants attacked the nearby crossing point."It was like everything was on fire," he said, showing a video on his mobile phone of heavy shelling.Philippine army officials said hope remained for an easing of the situation despite the standoff with the Philippine peacekeepers and the lack of knowledge of the precise whereabouts of the Fijians.The Philippine Foreign Ministry called on the United Nations "to exert every effort to ensure the safety and security of all peacekeepers in UNDOF", which consists of Indian, Nepalese, Irish and Dutch troops, as well as the Fijians and Filipinos.