JERUSALEM — Israel's military chief of staff has toured the Golan Heights a day after three Syrian tanks entered a demilitarized zone set up in a 1974 disengagement treaty between the sides.

Lt. Gen. Benny Gantz told Israeli soldiers there Sunday to be on high alert, warning that violence from Syria's civil war might reach Israel.

Israel made a complaint to UN peacekeepers on Saturday, a military spokesman said.

The foray would be the first such violation in 40 years and hikes concerns that violence from Syria's civil war could heat up a long-quiet frontier.

Israel's relatively low-key response of turning to the UN suggested it did not see the Syrian armour as an immediate threat.

But the entry marks the most serious spillover of Syria's turmoil at the frontier to date. Misfired Syrian shells have exploded inside Israel on several occasions and a tourist site was temporarily closed after armed Syrians were spotted nearby recently.

The three tanks entered the DMZ on Saturday, an Israeli military spokeswoman said, speaking on condition of anonymity in line with military protocol. She did not elaborate on what the tanks were doing.

The Israeli news site Ynet said the tanks and two armored personnel carriers drove a few kilometres away from Israeli military positions.

Israel captured the Golan Heights from Syria in the 1967 Mideast war. It later annexed the strategic territory overlooking northern Israel in a move that is not recognized internationally. Before 1967, Syria used the highlands to shell Israeli villages and farms.

The DMZ, which is about seven kilometres at its widest and 200 metres at its narrowest, was created after the 1973 war in which Syria tried to retake the plateau.

Marco Carminjani, an official with the UN body supervising the zone, said he could not immediately confirm the entry of the tanks. But if the report is true, he said, it would be a violation of the 1974 disengagement agreement between Syria and Israel. He said it would be the first such move in the zone since the accord.

There was no immediate comment from Syria.

Israel and Syria have been bitter enemies for decades and have fought several wars but the border has been mostly quiet for years.

There is concern in Israel that if the regime of Syrian President Bashar Assad is toppled, the country could fall into the hands of Islamic extremists or descend into sectarian warfare, destabilizing the region.

Israeli officials have also expressed concern that the frontier region could turn into a lawless area like Egypt's Sinai desert, where Islamic militants have gained strength since the ouster last year of Egyptian President Hosni Mubarak.

Syrian rebels launched a dawn assault Saturday on a strategic airbase in the north of the country, trying to disrupt strikes by warplanes and helicopters that pound rebel-held towns and give the regime of President Bashar Assad a major edge in the civil war.

The assault, reported by activists, comes a day before the start of a key international conference in Qatar at which the United States and its allies aim to reorganize the opposition's political leadership and unite their ranks. The leadership-in-exile has been widely seen as ineffective and out of touch with rebel fighters on the ground..

Rebel forces attacked the Taftanaz airbase early Saturday morning in fighting with government forces that continued into the afternoon, the anti-regime activist Syrian Observatory for Human Rights said.

Joining Syrian rebels in the attack were fighters from Jabhat al-Nusra, an al-Qaeda-inspired Islamic militant group made up of foreign jihadis, according to the Observatory. Al-Nusra fighters, who are considered among the most experienced and disciplined among the opposition forces, have led attacks on other airbases in the north in past months.

The Taftanaz base mainly houses military helicopters, near the main highway between the capital Damascus and the northern city of Aleppo, where rebels and the military have been battling for control for months.

Activists say more than 36,000 people have been killed in Syria since the anti-government uprising began in March 2011.

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  • A destroyed house from Syrian government forces shelling, at Jouret al-Shiyah, in Homs province, Syria, Thursday, Oct. 18, 2012. (AP Photo/Lens Yong Homsi)

  • In this Wednesday, Oct. 17, 2012, photo, Syrians rescue people from under the rubble of a destroyed building that was attacked by a Syrian force airstrike, at Kfar Nebel town, in Idlib province, northern Syria. (AP Photo/Idlib News Network ENN)

  • In this Wednesday, Oct. 17, 2012, photo, Syrian citizens remove copies of the Quran, the Muslims holy book from under the rubble of a destroyed mosque that was destroyed due to government forces shelling, at Kfar Nebel town, in Idlib province, northern Syria. (AP Photo/Idlib News Network ENN)

  • In this Wednesday, Oct. 17, 2012, photo, a Syrian man searches for people from under the rubble of a building that was destroyed by a Syrian force airstrike, at Kfar Nebel town, in Idlib province, northern Syria. (AP Photo/Idlib News Network ENN)

  • In this Wednesday, Oct. 17, 2012, photo, Syrian citizens gather to rescue people from under the rubble of a building that was destroyed from a Syrian force airstrike, at Kfar Nebel town, in Idlib province, northern Syria. (AP Photo/Idlib News Network ENN)

  • A destroyed house from Syrian government forces shelling, at Jouret al-Shiyah, in Homs province, Syria, Thursday, Oct. 18, 2012. (AP Photo/Lens Yong Homsi)

  • A general view of destroyed houses which was damaged by Syrian government forces shelling, at Baba Amr neighborhood, in Homs province, Syria, Thursday, Oct. 18, 2012. (AP Photo/Lens Yong Homsi)

  • In this Wednesday, Oct. 17, 2012, photo, Free Syrian Army fighter, Bashar al Hajji, points towards the besieged Shiite village of Zahraa in Aleppo, Syria. (AP Photo/Rob Celliers)