The United States demanded on Tuesday Syria withdraw its troops from Lebanon and stop its alleged support of terror.

"The (UN) Security Council resolution that was passed last September was very clear in terms of what the expectations are with regards to Lebanon. It stated very clearly that foreign troops need to be withdrawn from Lebanon," White House spokesman Scott McClellan said at a briefing.

"Syria's continued presence in Lebanon is a destabilizing force in the region and a destabilizing force in Lebanon. Syria's continued support for terrorism is a problem, it is a concern that we have expressed directly to the government of Syria," he said.

Syria has maintained some 14,000 troops and intelligence officials in Lebanon in disregard of the UN resolution.

"Syria needs to change its behavior and use its influence in a constructive way to do what it can to prevent attacks like this from happening in the first place," McClellan added.

The United States made the demand after a huge explosion in Beirut on Monday killed former Lebanese Prime Minister Rafik Hariri and 14 other people. This was believed to be the worst attack in the Lebanese capital since the end of the 1975-1990 civil war.