The attack came as Israel voiced fears that Syrian missiles and chemical weapons could fall into the hands of militants such as Lebanon's Hezbollah.
It is not clear what the convoy was carrying, but the latest reports suggest it was attacked on the Syrian side.
There has been no comment from Israel.
BBC Middle East correspondent Wyre Davies says the reports are impossible to verify, although some well-placed diplomats and military sources say they would not be surprised if Israel had acted, given the recent instability in Syria.
The Lebanese military and internal security forces have not officially confirmed the reports, but say there has been increased activity by Israeli warplanes over the country in the past week, and particularly in recent hours.Iran threat
One report suggested there were fears in Israel that Syria and Hezbollah would take advantage of the overcast weather conditions to send weaponry across the border.
The Associated Press quoted a US official as saying the strike hit a convoy of lorries carrying Russian-made SA-17 anti-aircraft missiles.
A Lebanese army spokesman denied there had been any attack on Lebanese territory, according to L'Orient Le Jour newspaper. Others said an attack took place near the town of Zabadani in southern Syria.
Correspondents say an attack on the Syrian side would cause a major diplomatic incident, as Iran has said it will treat any Israeli attack on Syria as an attack on itself.
The attack came days after Israel moved its Iron Dome defence system to the north of the country.
Correspondents say Israel fears that Lebanese Shia militant group Hezbollah could obtain anti-tank and anti-aircraft missiles, thus strengthening its ability to respond to Israeli air strikes.
Israel has also joined the US in expressing concern that Syria's presumed chemical weapons stockpile could be taken over by militant groups.
Vice Prime Minister Silvan Shalom told Israeli radio on Sunday that any sign that Syria was losing its grip on the weapons could lead to Israeli action, even a pre-emptive strike.
Analysts say Israel believes Syria received a battery of SA-17s from Russia after an alleged Israeli air strike in 2007 that destroyed a Syrian nuclear reactor.
The US government said in 2008 that the reactor was "not intended for peaceful purposes".