The powerful bomb Wednesday killed Antoine Ghanem, an anti-Syria lawmaker, and six others in a Christian neighborhood of Beirut - and threatened to derail efforts to bring the country's rival parties together to agree on a head of state ahead of time, before voting is set to begin next week.
At least 67 were wounded in the explosion, which severely damaged buildings and set cars ablaze during rush hour on a busy street in the Sin el-Fil neighborhood.
Ghanem, 64, a member of the Christian Phalange party, had returned from refuge abroad only two days earlier. He was the eighth anti-Syria figure and fourth governing coalition lawmaker to be assassinated in less than three years.
Coalition members blamed Syria for the death, but Damascus denied involvement, as it has for the previous seven assassinations, including the 2005 bombing death of former Prime Minister Rafik Hariri.
Prime Minister Fuad Saniora asked the United Nations secretary-general in a letter to add the Ghanem assassination to an international probe into Hariri's slaying and other political crimes in Lebanon.
Schools, universities and banks across the country as well as many businesses in Christian areas of Beirut and in the Mount Lebanon region north of the capital were closed Thursday for a day of mourning and to observe a strike called by the Phalange Party. A funeral was to be held Friday.
Saniora pledged that Lebanon would not be cowed by the assassination and would press ahead to pick a president.
"The hand of terror will not win and will not succeed in subduing us and silencing us," he said in a statement late Wednesday carried by the official news agency. "The Lebanese will not retreat and will have a new president elected by lawmakers, no matter how big the conspiracy was."
A Cabinet statement on Thursday vowed that terrorism will not prevail, and the killers would be found. It stressed that presidential elections should be held and called on lawmakers to attend Tuesday's session.
Russian President Vladimir Putin and German Chancellor Angela Merkel had had a few fights and used strong language because of the Ukrainian crisis in 2014