Saudi Arabia added a key Arab voice yesterday to mounting demands that Syria withdraw its troops swiftly from Lebanon, where they have helped secure it powerful influence for decades.

Syrian President Bashar al-Assad flew to Riyadh for crisis talks where Saudi Crown Prince Abdullah told him immediate action was needed.

Mr Abdullah, a regional ally of the United States, told Mr Assad that "Syria must start withdrawing soon, otherwise Saudi-Syrian relations will go through difficulties," one Saudi official said.

Russia, long one of Syria's best friends, also said the troops should go - a change for a country that abstained when the UN Security Council passed a US-inspired resolution to that effect in September.

Syria has faced growing calls to end its military and political dominance of its small neighbour since former Lebanese Prime Minister Rafik Hariri was assassinated last month in a Beirut bombing.

Lebanon's opposition blamed Syria and organised mass protests which toppled Beirut's pro-Syrian government this week. Damascus denies any involvement.

Mr Hariri had close personal ties with the ruling Saudi royal family, took Saudi citizenship and spent two decades in the country where construction deals turned him into one of the world's richest men.

"They know what they should do. They should withdraw immediately," another Saudi source said of the Syrians. "This is what we told them and this is what the whole world is telling them."

Saudi Foreign Minister Saud al-Faisal, who diplomats said attended the meeting in Riyadh, earlier told reporters in Egypt his country had "no initiative" to resolve the Syria-Lebanon crisis.

Pressure on Damascus had intensified on Wednesday when ally Russia cautiously threw its weight behind the pullout campaign.

"Syria should withdraw from Lebanon, but we all have to make sure that this withdrawal does not violate the very fragile balance which we still have in Lebanon, which is a very difficult country ethnically," Foreign Minister Sergei Lavrov said on Wednesday.