Damascus: Fearful of Israeli assassination, the top Hamas leaders who operate out of Syria are living on the run.

They change safe houses almost every night and no longer appear in public. They have cancelled all travel outside Syria and stopped using cell phones.

Khalid Mesha'al, the head of Hamas's political bureau and the man Israel accuses of thwarting the release of a kidnapped Israeli soldier in Gaza, is taking unprecedented security precautions, according to a Palestinian official in Damascus.

Meshaal, who survived an Israeli assassination attempt in 1997, already had strict security, travelling in armoured cars and rarely appearing in public.

"The Hamas leadership realises that it could be targeted," said the official. "It is taking all the precautions that can be taken."

Under international pressure in 2004, Syria forced Hamas to close their offices in Damascus. But the group's leaders still operate freely in the Syrian capital, and they frequently meet top Syrian officials including President Bashar Al Assad.

Israeli leaders warned the Syrian regime again on Monday that it could be targeted if the abducted soldier, Cpl Gilad Shalit, is killed.

"We know how to strike those who are involved," said Israeli Defence Minister Amir Peretz.

"I suggest that Bashar Assad, who is trying to operate with his eyes shut tight, open his eyes, because he is responsible."