Three sorties by 12 Israeli jets mounted the strike in the early hours yesterday, hitting a convoy as it carried heavy weaponry along a mountain track close to where the main Damascus- Beirut highway crosses the border.
Its load is thought to have included anti-aircraft missiles bound for Hizbollah in Lebanon. Sources said the jets had fired directly into Syrian territory, Israel's first such intervention in the country's two-year civil war.
The strike came as senior Israeli officials warned that after the week-long attack on Hamas targets in Gaza in November, new cross-border operations were being designed to neutralise Hizbollah's military threat.
Hizbollah and Hamas are Iran's main proxies in their struggle against Israel and are said to be under orders to hit back if the long-expected Israeli raids on Iran's nuclear facilities take place.
The main target of yesterday's air strike included SA-17 anti-aircraft missiles, an advanced Russian make that would threaten Israel's all-important air supremacy in the event of conflict, according to the Associated Press.
However, Israel is also concerned about the threat of some of Syria's chemical weapons ending up in the hands of Hizbollah extremists, particularly if the Assad regime begins to crumble.
In keeping with its usual policy, Israel refused to confirm reports of the strike last night and there was no comment from Syria.
However, Lebanese officials accused the Israeli air force of making three incursions into its air space on Tuesday afternoon and evening and again in the early hours of yesterday.
Benjamin Netanyahu, the Israeli prime minister, has sharpened his rhetoric over Syria in the past month, warning that the country might have to take action to stop Mr Assad's chemical weapons being transferred to Hizbollah.
"We must look around us, at what is happening in Iran and its proxies and at what is happening in other areas, with the deadly weapons in Syria, which is increasingly coming apart," Mr Netanyahu said.
One Israeli diplomat said that Hizbollah represented "the next step" for Israel after the Gaza conflict. (© Daily Telegraph, London)