(Adds Qatar acting as mediator over Fijians, UN official denies Filipinos ordered to surrender arms)
* Fijian peacekeepers held by Islamist group
* Filipino U.N. troops reach freedom at weekend
* Syrian war reaches frontier with Israel
By Baz Ratner and Manuel Mogato
EIN ZIVAN, Golan Heights/MANILA, Sept 1 (Reuters) - Heavy fighting erupted on Monday between the Syrian army and Islamist rebels on the Golan Heights, where 44 peacekeepers from Fiji are being held by militants and scores of their fellow blue helmets from the Philippines escaped after resisting capture.
Syria's three-year civil war reached the frontier with Israeli-controlled territory last week when Islamist fighters overran a crossing point in the line that has separated Israelis from Syrians in the Golan Heights since a 1973 war.
The fighters also turned against the U.N. blue helmets from a peacekeeping force that has patrolled the ceasefire line for 40 years. After the 44 Fijians were captured on Thursday, more than 70 Filipinos were besieged at two locations for two days.
All the Filipinos reached safety over the weekend. Thirty-two were rescued from one outpost on Saturday and 40 escaped from the other position early on Sunday while rebels were sleeping after a seven-hour firefight.
Fiji says it is negotiating the release of its 44 troops. The United Nations says it is not sure where they are being held. The Nusra Front, Syria's affiliate of al Qaeda, says it is holding them because the U.N. force protects Israel.
A senior Gulf official and a rebel commander close to Nusra Front said Qatar was acting as a mediator in talks to secure the Fijians' release.
It was not immediately clear on Monday whether forces loyal to Syrian President Bashar al-Assad had managed to retake control of the Quneitra crossing from the Nusra Front rebels.
Persistent gunshots and explosions from mortar shells and other munitions could be heard on the Israeli-occupied side of the frontier and combatants could be clearly seen targeting each other with their weapons.
At least one tank belonging to the Syrian army was also involved and some rebels could be seen a few metres (yards) away from the frontier fence.
A large Syrian flag that had been flying for days between the Quneitra crossing and the abandoned town was taken down and a United Nations position in the area, thought to be unmanned, was pounded with mortar shells.
The Syrian Observatory for Human Rights, which monitors violence in the Syrian civil war, said the Nusra Front and allied fighters were battling government forces near the Quneitra crossing and in the nearby village of al-Hamiydiah.
The Observatory said there were casualties on both sides. Observatory founder Rami Abdelrahman told Reuters the Nusra Front's aim appeared to be "to end once and for all the regime's presence in the area and it also appears that the goal is to expel the international observers".
UN OFFICIAL DENIES ORDERING FILIPINOS TO SURRENDER
The U.N. peacekeeping force in the area, known as UNDOF, includes 1,223 troops from India, Ireland, Nepal and the Netherlands as well as the Fijians and Filipinos who came under attack last week.
The Filipino blue helmets had been besieged in outposts known as positions 68 and 69 until their rescue from one on Saturday and escape from the other early on Sunday morning. The United Nations said both Syria and Israel helped in the rescue.
The Filipino army chief, General Gregorio Catapang, said his men had defended themselves in defiance of an order from their U.N. commander, who had told them to surrender their weapons to prevent harm befalling the captured Fijians.
"The UNDOF commander wants to save the Fijians at the expense of the Philippines," Catapang told reporters at the main army base in Manila after speaking to Filipino soldiers on the Golan Heights by Skype.
However, a senior U.N. official said no order to surrender their weapons had been given to the Filipinos.
The United Nations has announced that the Philippines will pull out of UNDOF. Austria, Japan and Croatia have also pulled their troops out of the force because of the deteriorating security situation as the civil war in Syria reaches the Golan.
On Sunday, Israel's military said it had shot down a drone that flew from Syria into Israeli-controlled airspace over the Golan. It was not immediately clear who had dispatched the unmanned aircraft or the nature of its mission in an area where fighting from Syria's civil war has occasionally spilled over into Israeli-held territory.
In a statement, the military said the drone was downed by a Patriot missile near the Quneitra crossing. (Additional reporting by Tom Perry in Beirut; Writing by Peter Graff; Editing by Giles Elgood)