By Dominic Evans
BEIRUT (Reuters) - Syria said its troops destroyed an Israeli vehicle that crossed into its territory from the Israeli-occupied Golan Heights on Tuesday and warned that any attempt to violate its sovereignty would meet "immediate and firm retaliation".
Israel said the incident took place on its side of the Golan ceasefire line, that the vehicle was damaged but not destroyed, none of its soldiers were hurt and they returned fire.
The clash highlighted the potential for renewed conflict along a frontline that has become increasingly fraught after nearly four decades of calm overseen by Syrian President Bashar al-Assad and his father.
It also followed Israeli airstrikes near Damascus against suspected missile stockpiles two weeks ago, after which Syria threatened to retaliate.
Assad is battling a two-year-old uprising in which rebel forces, including radical Islamists, have taken swathes of rural territory and attacked army posts near the Golan frontier.
There are frequent reports of cross-border gunfire from Syria during clashes between army and rebel forces but Tuesday's incident was the first time since the start of the crisis that Syria's armed forces said they targeted Israel's military.
"Our noble armed forces destroyed an Israeli vehicle ... which entered from the occupied territories and crossed the ceasefire line," Syria's military leadership said in a statement broadcast on state media. The incident occurred at 1:10 am (2210 GMT, Monday), it said.
Shortly afterwards, Israeli forces fired two rockets towards a Syrian position, without causing any casualties, Syria said.
The Israeli military's chief of staff, Lieutenant-General Benny Gantz, said the Israeli army vehicle had been patrolling on the Israeli side of a border fence when it came under repeated fire.
"They fire on it once. They fire on it twice. They fire on it a third time, from a clear Syrian position," he said in a speech. "One time, okay. Two times, okay. Three times, too many. The position was destroyed."
Defence Minister Moshe Yaalon said: "Our policy on Syria is clear: We are not intervening there, of course, in the civil war ... But as for the situation in the Golan Heights, we are not allowing and we will not permit a spillover of fire into our territory."
Tension in the Golan Heights region has been fuelled by the fighting on the Syrian side and several recent abductions by rebel fighters of U.N. peacekeepers, who have monitored a narrow zone of separation between Syrian and Israeli troops since 1974.
The abductions led the Philippines government to say it was considering withdrawing its troops from the UNDOF observer mission. Austria, the other main troop contributor, is concerned that French and British calls to drop an EU arms embargo on Syrian rebels would render its continued presence untenable.
Adding to the sense of alert, the militant Popular Front for the Liberation of Palestine said two weeks ago it was forming combat units to try to recapture the Golan, after Assad and Lebanon's Hezbollah said they would support such operations.
The announcement followed Israel's air strikes near Damascus against suspected missiles stocks destined for Hezbollah, which fought a 34-day war with Israel in 2006.
Syria's Foreign Ministry sent a written complaint to the United Nations on Tuesday, saying Israel's actions violated the United Nations charter and a 1974 military disengagement agreement between the two foes.
Syria's military command said the incident showed that Israel was supporting the anti-Assad rebels and aimed "to raise their morale which collapsed after the tough blows struck by our noble armed forces ... especially in Qusair."
Syria's army, backed by Hezbollah, has launched an offensive to capture the central town of Qusair, which has been in rebel hands for most of the two-year uprising which has now killed more than 80,000 people, according to the United Nations.
"The blatant Zionist aggression confirms that any violation, or attempted violation of the country's sovereignty will be met with immediate and firm retaliation," the Syrian army said.
(Additional reporting by Allyn Fisher-Ilan and Jeffrey Heller in Jerusalem; Editing by Robin Pomeroy)