A projectile from fighting in the Syrian civil war struck the Israeli-occupied Golan Heights on Thursday, and Israeli forces responded by attacking a Syrian army position, the military said.

In a statement, the military said it appeared the shooting from Syria was "errant fire" from battles between forces loyal to Syrian President Bashar al-Assad and rebels trying to topple him.

Such fighting, now in its fourth year, has often spilled over into Israeli-held parts of the Golan Heights, territory Israel captured from Syria in the 1967 Middle East war.

The military said that in response to the latest fire from the Syrian side of the frontier, "the IDF [Israel Defence Forces] targeted a Syrian army position, and hits were confirmed."

It did not say what type of attack Israel carried out. The Syrian Observatory for Human Rights said it was an air strike on a Syrian army base on the Golan. There were no immediate reports of casualties from either side.

Islamist fighters battling the Syrian army last week overran a UN-controlled crossing point on the "disengagement line" that has separated Israelis from Syrians on the Golan Heights since the 1973 Arab-Israeli war.

The fighters then turned against UN blue helmets from a peacekeeping force that has patrolled the zone since 1974. After 45 Fijians were captured on Thursday, 72 Filipinos were besieged by militants at two other locations for two days before the peacekeepers escaped.

The militants, believed to be part of an al-Qaeda-linked group known as Nusra Front, are still holding the 45 Fijian members of the United Nations' UNDOF Golan Heights force.

On Sunday, an Israeli Patriot missile shot down what the military described as a Syrian drone over the strategic plateau.

Cause for concern

The push into the Golan by the Nusra Front comes just two weeks after Israel ended a 50-day war against Hamas on its southern border with the Gaza Strip, giving the conflict-weary nation another cause for concern.

Last week's seizure of the strategic Quneitra border crossing by a mix of rebels — including the Nusra Front, fighters of the Western-backed Free Syrian Army and others — has created an unprecedented situation that has brought the extremists to within just a few metres of Israeli positions.

Israel captured the Golan, a plateau overlooking northern Israel, from Syria in the 1967 Mideast war. It later annexed the area, a move that has never been recognized internationally. Since the aftermath of the subsequent 1973 war, UN monitors have helped to enforce a stable truce and the area has been tense but generally quiet.

That started to change when the Syrian uprising erupted in March 2011, and the frontier has grown more volatile as the conflict has escalated into a complex and bloody civil war.

Israel has largely stayed on the sidelines of the war, quietly content to see Assad's forces tied down by battles with various rebel groups trying to oust him. However, Israel has occasionally responded to mortar fire that spilled over the border, usually unintentionally, and is believed to have carried out several airstrikes on weapons shipments thought to be bound for Hezbollah militants in Lebanon.

With files from Associated Press