The threat of the intensifying war in Syria dragging in Israel has grown with the Damascus regime's withdrawal of thousands of troops from the disputed Golan Heights to reinforce the beleaguered Syrian capital.

This pullback, the largest withdrawal of forces from the Syrian-held sector of the strategic plateau in four decades, has left a military vacuum on Israel's northern frontier that's reportedly being filled by the jihadist rebels of Jabhat al-Nusra, or the al-Nusra Front.

The Israelis have repeatedly said they do not want to get involved in the Syrian bloodbath, in which by U.N. count more than 70,000 people have been killed.

But the Syrian pullback dramatically alters the strategic situation on the Golan for the Israelis, who captured the western sector of the 3,000-foot volcanic plateau in the 1967 Middle East war.

Before Syria's civil war erupted in March 2011, the Syrian-held eastern sector was understood to have been manned by four army divisions.

That made it the safest of Israel's borders because the regime wanted to avoid any conflict with Israel after the 1973 Yom Kippur War, when the Syrians came within an ace of recapturing what they'd lost in 1967.

Reports in Israel indicate the regime of President Bashar Assad had pulled out two divisions -- around 20,000 troops -- to bolster the defense of Damascus.

"They've moved some of their best battalions away from the Golan," a Western diplomatic source observed.

"They've replaced some of them with poorer quality battalions which have involved reducing manpower. These moves are very significant."

The withdrawal and the growing encroachment by rebel forces also threatens the 1,200-strong U.N. observer force stationed on the Golan since 1967. Several countries have already withdrawn their contingents.

The al-Nusra Front is the most powerful and most effective of the jihadist groups fighting in the two-year-old uprising to topple Assad and has been closely linked to al-Qaida in Iraq.

Indeed, the leader of al-Qaida's Iraqi wing, the Islamic State of Iraq, Abu Bakr al-Baghdadi, announced in a statement posted on Islamist websites Tuesday that the two groups had united.

He said they would now operate under a new name, "the Islamic State of Iraq and the Levant."

It's not clear whether this will mean the al-Nusra Front will be significantly reinforced in the Golan region, from where the rebels want to open a new front against Damascus, by battle-hardened fighters from Iraq, Syria's eastern neighbor.

But even without such reinforcement, the Israelis are becoming increasingly concerned that the jihadists, who've sworn to "liberate" Jerusalem from Israeli rule, could turn their focus southward if they succeed in storming Damascus, the seat of the regime's power -- and possibly even if they don't succeed.

Israeli concerns have been eased somewhat by a joint Saudi Arabia-U.S. operation to build up more secular rebel forces in Jordan, Syria's southern neighbor, to counter the jihadist groups in southern Syria and prevent Damascus falling into the Islamists' hands.

But al-Nusra appears to be moving east toward the Jordanian border, and in recent days has overrun a Syrian army base and several smaller installations across southern Syria.

That puts the jihadists in control of an area that borders both the Israeli-held section of the Golan and Jordan to the east,

Israel's new defense minister, former Gen. Moshe "Bogie" Yaalon, inspected Israeli defenses on the Golan last week with Chief of Staff Lt. Gen. Benny Gantz, underlining Israeli concerns for the northern border.

Yaalon, a right wing hardliner and chief of staff himself in 2002-05, said the Israelis were particularly anxious about the al-Nusra Front getting its hands on Syria's arsenal of chemical and biological weapons.

The day before Yaalon's inspection, al-Nusra forces in northern Syria were reported to be converging on two of the Syrian regime's biggest CW depots, the al-Safira military and air-defense base near Aleppo, and the Dumeir complex 25 miles northeast of Damascus in the south.

"We'll act to ensure that these types of weapons do not reach irresponsible hands," Yaalon warned.

The Israeli air force bombed a CW base northwest of Damascus and close to the Lebanese border Jan. 30, reportedly destroying a convoy believed to transporting chemical arms to Hezbollah, a key regime ally, in Lebanon.