Syria says it will leave Lebanon before the country's general election in May.
A date for a full withdrawal of Syrian troops has not yet been given
"We will withdraw as soon as possible, without delay and probably a long time before the election," said Imad Moustapha, Syrian ambassador to the US.
Syrian troops have already begun pulling out of southern and northern Lebanon, Lebanese officials say.
Lebanese President Emile Lahoud is due to begin talks with parliamentary deputies after which he is expected to name a new pro-Syrian prime minister.
Mr Lahoud holds a parliamentary majority and correspondents say the consultations are likely to preserve Syria's political influence in Lebanon for the time being.
On Tuesday, hundreds of thousands of people gathered in Beirut to back Syria's role in the country, a demonstration which dwarfed earlier anti-Syrian protests.
Meanwhile, US President George W Bush has repeated demands for Syria to leave.
"All Syrian military forces and intelligence personnel must withdraw before the Lebanese elections for those elections to be free and fair," Mr Bush said.
Otherwise, he added, Syria would become "even more isolated from the world".
Imad Moustapha told the BBC that even though Syria knew "that the overwhelming majority of the Lebanese are pro-Syrians" it had always maintained that "the moment we believe that our presence in Lebanon will create a rift among the Lebanese people, we will leave".
"We will withdraw every single Syrian soldier, but we will do this in a phased, organised way, so that we do not create any vacuum or chaos behind us," Mr Moustapha told the World Today programme.
He said Syrian troops would be pulled back to the Syrian Lebanese border region in the Bekaa Valley before the end of March and then pulled out of Lebanon altogether.
No exact date has been given for a full Syrian withdrawal.
Mr Moustapha rejected US pressure and said Syria had already undertaken democratic reforms and the process would be speeded up with the withdrawal from Lebanon and the resources that would be freed.
He said: "There are many ways to introduce democracies. You can send your troops, your armies, and you can destroy whole country like Iraq and then you can say 'Look we have introduced democracy'."
"Instead of sending your troops and your jet fighters and your cruise missiles, help Syria evolve towards a more free and more democratic society, which is what we are doing and what we plan to do."
SYRIA IN LEBANON
Military intervention begins in 1976
30,000 troops in Lebanon during 1980s, currently 14,000
Syrian forces help end Lebanese civil war in 1990 and maintain peace
Calls for Syrian withdrawal increase in 2000 after Israeli pullout from southern Lebanon
UN resolution calling for foreign forces' withdrawal in Sept 2004
Hours earlier, the head of the Syrian-allied Hezbollah group had warned the US, which has been leading demands for a Syrian withdrawal, not to interfere in Lebanon.
Organised by Hezbollah, a powerful political and military organisation of Shia Muslims, Tuesday's demonstration dwarfed previous opposition protests urging Syrian troops to leave.
Hassan Nasrallah said there would be further demonstrations in other Lebanese towns, including Tripoli in the north, Nabatiya in the south and in the eastern Bekaa valley.
Syrian troops arrived in neighbouring Lebanon as peacekeepers during the 1975-1990 civil war. Since then, Damascus has kept a firm hold on the political and financial spheres in Lebanon.
France, Germany and Russia have also called for a Syrian withdrawal, as has its long-standing Arab ally, Saudi Arabia.
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