Banks, schools and government offices are closed in Lebanon, as the country mourns an anti-Syrian MP who was killed in a car bombing in the capital Beirut.
PM Fouad Siniora said his country would not be silenced by the blast
Antoine Ghanim, of the Maronite Phalange party, died with at least six others in the blast in the mainly Christian Sin al-Fil district.
World leaders have condemned the assassination, while several Lebanese politicians blamed Syria for the bomb.
Lebanon is poised to choose a successor to pro-Syrian President Emile Lahoud.
But the country has been mired in an ongoing political crisis, with a deadlock between pro- and anti-Syrian factions in parliament.
'Hand of terror'
Mr Ghanim's Phalange party called for a strike and day of mourning on Thursday.
The education ministry said schools and universities would remain closed again on Friday, when a funeral would be held for Mr Ghanim.
Prime Minister Fouad Siniora vowed to press ahead with the presidential vote, saying his country would not be silenced.
He has called for a UN investigation into the assassination of Mr Ghanim, who had returned to Beirut just a few days before his death to take part in the vote.
"The hand of terror will not win and will not succeed in subduing us and silencing us," Mr Siniora said.
"The Lebanese will not retreat and will have a new president elected by lawmakers, no matter how big the conspiracy was."
Lebanon's anti-Syrian ruling coalition and its opposition are still making positive noises about the need for dialogue and understanding, says the BBC's Jim Muir in Beirut.
But the assassination makes it even less likely that a deal will be reached on a new president before Tuesday's crucial vote, our correspondent says.
Syria said it had no involvement in the attack, calling it a "criminal act" that undermined hopes for Lebanese national reconciliation.
Feb 2005: Ex-PM Rafik Hariri
April 2005: MP Bassel Fleihan
June 2005: Anti-Syria journalist Samir Kassir
June 2005: Ex-Communist leader George Hawi
Dec 2005: Anti-Syria MP Gebran Tueni
Nov 2006: Industry Minister Pierre Gemayel
June 2007: Anti-Syria MP Walid Eido
Sep 2007: Anti-Syria MP Antoine Ghanim
But some Lebanese politicians were quick to blame Damascus for the blast.
Saad Hariri, son of Rafik Hariri, a former prime minister who was assassinated in a bomb attack in 2005, said responsibility lay with the "cowardly regime" of Syria.
Even pro-Syrian Mr Lahoud said it was no coincidence someone was killed whenever there were positive developments in Lebanon.
US President George W Bush denounced the "horrific assassination", which he described as attempts by Syria and Lebanon to destabilise Lebanon.
The attack has also been criticised by the UK, the EU, Russia, China, France and Italy.
Six other leading figures in Lebanon's anti-Syria movement have been killed since Rafik Hariri's assassination in 2005.
Syria has denied involvement in any of the killings.