Syria is expected to announce a partial withdrawal of its troops from Lebanon, a move many analysts saw as inevitable in the face of increasing world criticism.
It is thought President Bashar al-Assad will say some troops will quit completely, while some will move to the border.
World pressure has mounted since the assassination of former Lebanese Prime Minister Rafik al-Hariri – an attack widely blamed on Syria – although Damascus denies involvement.
But US President George W. Bush said a partial withdrawal is not enough.
He called for all forces to be out by May, to clear the way for free elections.
“There are no half measures involved. When the United States and France say withdrawal we mean full withdrawal, no half-hearted measures,” he said.
Hundreds of Lebanese held impromptu celebrations in the streets of Beirut when news of the predicted Syrian announcement leaked out.
Syria has carried out five troop deployments since 2000 but has continued to maintain soldiers in the capital and northern Lebanon.