Sophisticated weapons could be transferred from Syria to militant group Hezbollah and to Lebanon if the regime of Bashar al-Assad falls, Israel Defence Minister Ehud Barak warned on Thursday.

"You have to be alert to the possibility so that during the fall of the regime there will not be the transfer of sophisticated Syrian weapons to Hezbollah and Lebanon," he told Israeli military radio.

"We are tracking this issue constantly and carefully," he said, without giving further details.

Barak said Israeli assessments suggest Assad's downfall was a matter of time.

"The fate of the regime of Bashar al-Assad is sealed; his situation is getting worse every week," he said.

Israel has been closely following developments in neighbouring Syria, where Assad's regime has launched a violent crackdown against political opponents, leaving more than 6,000 dead, according to activists.

Israel fears it could suffer from various consequences of the regime's weakening and collapse, including a wave of refugees, or even attempts by the regime to distract attention by attacking the Jewish state.

Officials have also warned that Syria's weapons, including alleged chemical and biological ones, could fall into the hands of militants, including Hezbollah, which fought a war with Israel in 2006.

Last month, Major General Amir Eshel, the incoming chief of Israel's air force, said Syria possessed "huge stockpiles" of such weapons.

"The immediate concern is the huge stockpiles of chemicals, biologicals, strategic capabilities that are still going into Syria, mainly from eastern Europe," he said.

"That's a major concern because I don't know who is going to own those the day after. Up till now, what has been transferred to Hezbollah? What will be transferred to Hezbollah? What will be divided between those factions inside Syria? What is that going to create?"