Lebanon's president has asked the pro-Syrian former prime minister to form a new government, 10 days after he resigned amid anti-Syrian protests.
Huge rival demonstrations have been taking place in Lebanon
Shortly after his reappointment, Omar Karami called on all parties to join a government of national unity.
A majority of MPs had backed him to form a new cabinet, but the opposition complained their demands were ignored.
Lebanon's defence minister, meanwhile, has said thousands of Syrian troops have begun leaving Lebanon.
Abdul Rahim Mrad told Reuters news agency: "Most of those withdrawing are going to Syrian territory."
Last week, Syrian President Bashar al-Assad announced a two-stage withdrawal plan, after weeks of pressure to pull 14,000 troops and intelligence officers out of Lebanon.
Redeployment 'under way'
Reuters quoted witnesses as saying at least 115 Syrian military vehicles crossed the border into Syria on Wednesday night.
Syrian troops have also begun relocating from southern and northern Lebanon, to the Bekaa valley on the border between the two countries.
A stream of Syrian military trucks headed east throughout the day and troops were seen packing up camps and materiel in the mountains.
No date has been given for a full Syrian withdrawal, but Damascus says it will complete the pull-out before Lebanon's general election in May.
Lebanon's parliament backed Mr Karami's return after a huge rally in Beirut in support of Syria, which keeps a tight grip on power in Lebanon.
"The difficulties we all know cannot be confronted without a government of national unity and salvation," Mr Karami said.
"We will extend our hand and wait for the other side."
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
The BBC's Kim Ghattas in Beirut says the opposition is unlikely to participate in any cabinet unless the authorities give into some of its demands, including the withdrawal of Syrian troops.
The US has repeated calls for a full withdrawal of Syrian troops, and the United Nations is keeping up pressure by sending envoy Terje Roed-Larsen to the Damascus for talks.
The BBC's Dan Isaacs in Damascus says an opposition rally in the city has turned into a show of support for the government, as hundreds of people have taken to the streets carrying Syrian flags and posters of President Assad.
Syrian troops have been stationed in Lebanon since 1976. They were instrumental in stabilising the country following the 15-year civil war.
Pressure on Syria to withdraw intensified after the 14 February car bomb death of former Lebanese Prime Minister Mr Hariri.
Lebanese opposition groups accused Syria of involvement, although Damascus has strongly denied the charge.