Syria Rebels Seize Crossing Near Israeli Border, Activists Say BEIRUT - Austria said on Thursday it would pull out of a U.N. force on the Golan Heights after battles between Syrian troops and rebels there, in a blow to a mission that has kept the Israeli-Syrian war front quiet for 40 years. Israel is anxious for the international mission to remain in place, worried that the Golan will become a springboard for attacks on Israelis by Islamist militants fighting to oust Syrian President Bashar al-Assad. But the departure of the Austrians, who make up about 380 of the 1,000-strong United Nations Disengagement Observer Force (UNDOF), threatens the whole operation. "Austria has been a backbone of the mission, and their withdrawal will impact the mission's operational capacity," said U.N. spokeswoman Josephine Guerrero. Anti-Assad rebels briefly seized the sole crossing between Israel and Syria on Thursday morning, sending U.N. staff scurrying to their shelters, before Syrian soldiers managed to push them back and reassert their control of Quneitra. The rebel attack appeared to be an attempt to regain some momentum after Assad's forces, backed up by well-trained Lebanese Hezbollah guerrillas, on Wednesday seized control of Qusair, a town on a vital supply route close to Lebanon. Pro-government troops have won a string of successes in recent weeks, boosting Assad at a time when the United States and Russia are struggling to organise a peace conference aimed at ending the civil war, which has killed more than 80,000. Looking to ram home their victory, Assad's troops have turned their fire on villages northeast of Qusair, where hundreds of rebels and civilians were holed up, prompting one group of activists to issue a desperate plea for rebel support. God has given us the strength to persevere, but until when only God knows. We beg you to move as quickly as possible to rescue us," said a message posted on social networking sites. Shortly afterwards, Syrian television announced that the army had "restored security and stability" to one of the villages in its sights - Debaa. France, which earlier this week accused Assad of deploying nerve gas in the civil war, said on Wednesday the situation on the ground needed to be "rebalanced" after the fall of Qusair, but did not say how that could be achieved. Russia said on Thursday it was worried that allegations of gas attacks might be used as a pretext for foreign intervention. "I do not rule out that somebody wants to use it to state that a red line has been crossed and a foreign intervention is necessary," Russian Foreign Minister Sergei Lavrov told a news conference in Moscow with his German and Finnish counterparts. Western countries have so far shown little appetite for getting sucked into the Syrian conflict, but there is also a clear aversion to letting Assad, heavily backed by Shi'ite Iran and their Hezbollah associates, emerge victorious. France and Britain last month pushed the European Union to drop its ban on arming the rebels, who are mainly Sunni Muslims. London and Paris have not yet said if they plan to arm the fighters. They wanted the ban lifted to apply pressure on Assad. The International Committee of the Red Cross (ICRC) said it was negotiating with Syria to reach areas surrounding Qusair to deliver medical assistance to the wounded. Humanitarian groups have estimated that up to 1,500 people might need help. "Today the conflict is extremely fragmented, and this is one of the biggest operational challenges for the ICRC," said Robert Mardini, the head of ICRC operations in the Middle East. Qusair lies along a corridor through the central province of Homs, linking the capital Damascus to the coastal heartland of Assad's minority Alawite sect, an offshoot of Shi'ite Islam. Many rebels and civilians fled the battered town early Wednesday, heading to the villages of Debaa, 5 kilometres (3 miles) northeast, and Buwayda, another 7 km in the same direction. "We have a large number of civilians and wounded in Buwayda," said activist Mohammed al-Qusair. Russia, which has thrown its weight firmly behind Assad, to the frustration of the West, cautioned Damascus on Thursday that the conflict could only be resolved through diplomacy.