Security sources in Lebanon, including a Western diplomat, reported the attack on a column of trucks the Israelis suspected may have been carrying chemical weapons or advanced Russian-built, anti-aircraft missiles from Syria into Lebanon for Hezbollah, the powerful Iranian-backed group that's a key ally of the beleaguered regime in Damascus.
Lebanese military officials denied there was an airstrike but they had reported unusually heavy Israeli activity by air force jets over southern Lebanon between nightfall at around 5 p.m. Tuesday and 8 a.m. Wednesday.
They said there were three distinct groups of aircraft active in Lebanese airspace within that timeframe.
If there was an airstrike it would be the first offensive action mounted by Israel in Syria since the civil war there erupted March 15, 2011, with a pro-democracy uprising against the regime of President Bashar Assad.
Israeli officials declined comment but the reports followed unequivocal signs by Israeli officials that there was growing concern about how secure Syria's chemical weapons.
Israeli leaders harbor grave fears these will fall into the hands of anti-Israeli Sunni extremists fighting the minority regime dominated by Alawites, an offshoot of the Shiite sect that dominates Iran, Syria's key ally and Israel's bete noire.
Israeli Deputy Prime Minister Silvan Shalom disclosed Sunday that Israel could unleash military strikes at the first tangible sign the regime's control of the chemical weapons, which are stored in four depots across the country, is slipping.
In the meantime, Israel has quietly deployed two batteries of its Iron Dome counter-rocket system around the port city of Haifa in the north, covering the borders with Syria and Lebanon.
Israeli officials maintained the deployment was routine but this took place as Prime Minister Binyamin Netanyahu and his military chiefs were publicly warning that events appeared to be getting out of control in Syria.
On Monday, Netanyahu told visiting U.S. congressmen that his policy options for dealing with the Syrian bloodletting were "between bad, bad and worse," with worries over chemical weapons so close to Israel's borders the foremost concern.
Shalom noted that if Syrian rebels or Hezbollah, which fought a 34-day war with Israel in 2006, got their hands on these weapons "it would dramatically change the capabilities of those organizations.
That, he warned, would amount to "a crossing of all red lines that would require a different approach, including even preventive operations."
Israeli officials have said military commanders have drawn up plans for such contingencies.
The Israelis also fear that the Syrians, or Iranians through Syria, are giving Hezbollah sophisticated SA-17 anti-aircraft missiles that would allow the Lebanese fighters to challenge Israel's supremacy in the air over Lebanon for the first time.
Skeptics suspect the statements by Netanyahu and others were a politically motivated diversion to help him quickly form a new coalition after his narrow win in last week's parliamentary elections.
It wouldn't be the first time an Israeli prime minister has invoked security threats to give him political wiggle room.
But it has been Israel's nightmare for some time that Assad would lose control of Syria's reputedly large arsenal of chemical weapons, which might then be turned on Israel to counteract its formidable military power.
Another indication that Netanyahu may have been planning military action is that he has dispatched National Security Adviser Yaakov Amidror to Moscow to meet with Foreign Minister Sergey Lavrov.
Russia is a key backer of Assad, and has been crucial in covering Syria in the U.N. Security Council against international intervention.
On Saturday, Tehran cautioned that an attack on Assad's regime would be considered an attack on Iran.
Debkafile, an Israeli website widely believed to be linked to Israeli intelligence and too often disseminate disinformation, reported Saturday that senior Syrians and several ranking officers of Hezbollah and Iran's elite al-Quds Force were killed in a bombing in southern Syria near the Israeli border the day before.
It said eight men died in the mysterious double blast outside a regional intelligence HQ in Quneitra on the Golan Heights, half of which Israel has occupied since 1967. Debkafile didn't identify the perpetrators.