Israel recently conveyed a warning to Syria through a third party that it would hold Damascus accountable if Lebanese Hezbollah launched attacks on the Jewish state, Israeli and European sources said.

The sources, speaking on condition of anonymity, said the warning stemmed largely from Israeli concerns that Hezbollah would launch salvoes of cross-border rockets to coincide with any major Israeli offensive in the Hamas-controlled Gaza Strip.

The sources said the message was conveyed in February through at least one European intermediary following the assassination of a top Hezbollah commander and before this month's five-day Israeli offensive in the Gaza Strip in which more than 120 Palestinians, many of them civilians, were killed.

After the group's senior commander, Imad Moughniyah, was killed in a bombing in Damascus, Hezbollah leader Sayyed Hassan Nasrallah threatened Israel with 'open war'.

Shi'ite Muslim Hezbollah and its main backer, Iran, accused Israel of being behind the assassination, a charge Israeli Prime Minister Ehud Olmert's office denied in a rare public statement.

A European source familiar with the matter said the message conveyed to Damascus said Syria could be targeted by Israel even if Hezbollah's attack emanated from Lebanese soil.

An Israeli source with knowledge of government affairs said: 'The message was passed around late February, before the last round of fighting in Gaza.'

'It has become clear to us Syria has to understand there is a price for its use of proxy terrorism, especially as Damascus is itself a proxy - the long-arm of Iran,' the source said.

Another senior Israeli government official with knowledge of defence affairs declined comment on whether a message was sent to Damascus, but told Reuters: 'This is sound strategy. Syria has significantly deepened its involvement with Hezbollah in southern Lebanon since the war.'

Asked about the risk of an Israeli attack on Syria in response to a Hezbollah attack, a British official said: 'There is always a danger that a turn of events here could prompt something on the northern border, which would be a disaster.'

'The death of Moughniyah, the threatened Hezbollah retaliation does leave a spectre of a wider regional conflict,' the official said, playing down the chances of opening an Israeli-Syrian peace track under the circumstances.

'There's an interest on both sides but I think it's very difficult to move forward on it,' the official said, citing close ties between Syria and Iran. 'It's become far more difficult the idea of an Israeli-Syrian deal.'