After new clashes between Syrian troops and rebels in the Golan, and Austria's announced withdrawal from a UN monitoring force, Israel is concerned about security along its ceasefire line with Syria.

The army remained on high alert in the region on Friday, bringing up reinforcements of tanks and troops, and readying an anti-tank missile unit, media said.

That came after Austria said it would withdraw peacekeepers from the UN force, citing deteriorating security, and the Philippines said it was studying a similar move after one of its soldiers was wounded in the fierce fighting on Thursday.

The Quneitra crossing between the Israeli and Syrian sides of the armistice line was briefly seized by rebels and then recaptured by government troops following small-arms and artillery exchanges, a security source said.

An AFP correspondent saw tanks of President Bashar al-Assad's regime approaching the ceasefire line later in the day.

Israeli army spokesman Captain Arye Shalicar told AFP on Thursday: "We're watching very closely what's happening there, and we have to be ready for any development. We hope there won't be any spillover into Israel.

"It is very worrying because, on the one hand, you have jihadists and Islamists who are fighting there [on the rebel side] and, on the other hand, you also have government forces which are allied with [the Lebanese militant group] Hezbollah.

"We certainly don't want to have Hezbollah on two fronts," he said, referring to the presence of the group in southern Lebanon, next to the Israeli border.

Austria, which has been a cornerstone of UNDOF, said on Thursday it would withdraw its 377 soldiers, who make up more than a third of the force, because the threat to them had "reached an unacceptable level.
 

"The secured movement and supply of our troops on the Golan can no longer be guaranteed," added a joint statement from Chancellor Werner Faymann and Vice Chancellor Michael Spindelegger.

Israel reacted with dismay to the Austrian announcement, as the UN held emergency talks to replace its contingent.

"In light of Austria's announcement, there are questions over the stability of the 'border' between Israel and Syria," said Jacques Neriah, an Israeli reserves colonel and former military intelligence analyst.

He warned that the Filipinos "could follow the Austrians."

"The Security Council should therefore present a solution. And [although] Syria has no interest in having tension with Israel... we cannot leave the zone without observers," he said.