The Syrian President, Bashar al-Assad, is expected to announce a redeployment of troops in neighbouring Lebanon.
Protests against Syria have been going on for weeks in Lebanon
Officials said he will move soldiers back to Lebanon's eastern border with Syria, short of a full withdrawal.
On Friday, US President George W Bush and French President Jacques Chirac called on Syria to pull out completely.
Damascus is under international and Arab pressure to pull its army out of Lebanon, 30 years after it intervened to try to end a civil war.
Lebanese opposition groups have blamed Syria for a bomb attack in Beirut last month which killed former Prime Minister Rafik Hariri - a charge Damascus has strongly denied.
Mr Assad is expected to make the announcement in a rare speech to parliament on Saturday.
Hours before the anticipated address, Lebanese troops briefly deployed near the Syrian intelligence headquarters in Beirut, before withdrawing.
There was no prior indication of the move, and there is no clear reason why it was made.
In the city centre, hundreds of flag-waving Lebanese continued to protest against Syria, as they have done daily since the 14 February bombing.
The US said it has held talks with France and the United Nations to discuss ways of helping the Lebanese to establish political control once the Syrians have gone.
SYRIA IN LEBANON
Military intervention begins in 1976
30,000 troops in Lebanon during 1980s, currently 15,000
Syrian forces crucial in ending the Lebanese civil war in 1990 and maintaining peace
Calls for departure of the Syrians increase gradually with Israeli withdrawal in 2000
UN resolution calling for withdrawal of all foreign forces passed in Sept 2004
President Bush said the withdrawal must happen before Lebanese elections in May.
"When we say withdraw we mean complete withdrawal - no half-hearted measures," he said.
France, a traditional ally and former colonial ruler of Syria, has also toughened its stance.
President Jacques Chirac called on Friday for the "full, entire and immediate" implementation of a UN resolution seeking Syrian withdrawal from Lebanon.
Syrian troops entered Lebanon in 1976 and were backed by the Arab League as a peacekeeping force in the country's civil war. When the civil war ended in 1990, some 15,000 troops and thousands of intelligence personnel remained, overlooking Beirut and in north-western regions.
UN Security Council members have been considering measures against Syria since issuing a resolution in September calling for all foreign forces to leave Lebanon.
A 1989 agreement that ended the Lebanese civil war calls for a phased withdrawal of Syrian troops, beginning with redeployment to the eastern Bekaa Valley.
Although likely to fall short of a complete pull-out, Mr Assad's expected announcement may help to ease pressure if it is seen as a clear step towards a full withdrawal, says the BBC's Barbara Plett in Beirut.
Our correspondent says Syria is looking increasingly isolated as pressure mounts not only from the US and UK, but also from traditional allies like Russia, Saudi Arabia and France.