Israeli forces went on alert early Thursday as fighting broke out on the disputed Golan Heights in southern Syria, where Israel occupies part of the strategic plateau, between Syrian rebels and forces loyal to embattled President Bashar Assad.

The fighting centered on the main crossing point between Syrian territory and the occupation zone on the heights' western flank at Quneitra, the largely abandoned regional capital.

Many of the rebels "are foreign jihadists, many of them Iraqis," said analyst David Nisan who monitors the region for Israel's Max Security Solutions.

"This is the most tense the situation has been since 1973. Even a very tiny provocation could result in a regional deterioration."

Israel has been bracing for serious trouble on the 1973 war armistice line, which divides the Golan, for several weeks since Syrian rebel forces, including jihadist fighters sworn to eradicate the Jewish state, launched a southern offensive to outflank regime forces holding Damascus.

But one of Israel's worst fears is that Assad's key ally, the Iranian-backed Hezbollah movement from Lebanon, which drove Israeli forces out of south Lebanon in May 2000 to end a 22-year occupation, will launch a "liberation offensive" in the Golan.

Since the end of January, the Israeli air force has mounted three airstrikes against targets in Syria where advanced weapons, reportedly Russian-built SA-17 anti-aircraft missiles and Iranian Fateh 110 surface-to-surface missiles, were being transferred to Hezbollah by the Syrians.

Israel, keen to avoid a clash with Syria, has gotten word to Assad it's not seeking to harm his regime, only Hezbollah.

Syria hasn't retaliated for the airstrikes. Assad doesn't want Israel on his back as he struggles for survival though he has threatened action.

Indeed, in many ways Israel would have been content to leave Assad in power in Damascus.

His regime, and that of his late father, deliberately maintained quiet on the Golan, captured by Israel in 1967, since the 1973 war when Syrian forces came within an ace of driving the Israelis off the volcanic plateau.

Instead, Assad has used Hezbollah to maintain military pressure on Israel from Lebanon.

In July 2006, Hezbollah initiated a 34-day war with Israel that ended in a stalemate, but was seen as a defeat for Israel's mighty military.

Jihadist rebels operating in southern Syria are seen as a possible threat to Israel, most notably the al-Nusra Front, affiliated with al-Qaida, and the Yarmouk Martyrs Brigade.

But Hezbollah, heroes of the regime after its Iranian-trained fighters spearheaded the capture of the strategic town of Qusair in western Syria Tuesday, are widely seen as the most serious threat because it represents Tehran's military arm against Israel.

In recent weeks, Hezbollah has deployed thousands of fighters to prop up Assad, which meant Arabs fighting other Arabs, and that has not gone down well regionally.

The movement has lost much of the luster it acquired by driving Israel out of Lebanon, then battling it to a standstill in 2006 -- the first Arab organization ever to liberate Arab territory through force of arms.

Hezbollah leader Hassan Nasrallah has found himself facing heavy criticism for aiding a regime that's tormented Lebanon for decades.

But he's sought to get around this by portraying Hezbollah's growing involvement in Assad's war as an extension of the long-running conflict with Israel.

It's questionable whether Arabs at large believe that. Certainly few Lebanese do.

But more ominously for Israel -- and probably for tiny, dangerously vulnerable Lebanon as well -- Nasrallah said in a fiery May 10 speech Hezbollah, armed with advanced Iranian and Syrian weaponry, was being given free rein by Damascus to reignite the long-dormant Golan front.

He said Hezbollah would back "resistance groups" seeking to liberate the Golan while the weapons systems he'd get from Syria would upset the balance of power with Israel.

Portraying the Israeli airstrikes as proof the anti-Assad uprising is an Israeli-led plot, he said: "Syria's ... strategic response is to open the Golan front and to open the door to popular resistance in the Golan."

Israel doesn't particularly want a fight while a bigger crisis is brewing in Syria and Iran threatens the Jewish state.

It is hoping Hezbollah is too preoccupied saving Assad's hide to launch a new war.

The problem is Nasrallah, wily operator though he is, may have talked himself into crossing swords with Israel again.