Lebanese media outlets have confirmed the death of Mohamed Chatah, former finance minister and senior advisor to ex-Lebanese prime minister Saad Hariri, in a strong explosion in Beirut on Friday.
The blast went off a few hundred metres from the government headquarters and parliament building.
A health ministry source told Lebanon's Future TV channel that at least six people died in the attack, four of whom are still unidentified. Seventy-eight were injured, according to the Red Cross. The blast destroyed six buildings, 14 shops and 42 cars.
Security sources believe the blast was caused by a stolen Honda vehicle stuffed with 50-60 kilogrammes of explosives, Egypt's state news agency MENA reported.
Acting state prosecutor Samir Hammoud visited the bomb site on Friday afternoon.
Sakr Sakr, the Lebanese government's commissioner to the military tribunal, ordered military intelligence, military police, and the criminal evidence and information branch to launch a preliminary investigation into the attack.
Chatah was Lebanon's ambassador to Washington and a prominent economist. He served as an advisor to the government of ex-premier Fouad Saniora and his successor Saad Hariri whose father, Rafik, was assassinated in a massive car bomb in 2005.
According to AFP, he was killed as he headed to Saad Hariri's mansion in Beirut city centre to attend a meeting of the March 14 anti-Syria coalition which backs the Syrian opposition to the Assad regime.
Troops were seen deploying nearby, and ambulances were rushing to the area.
Future TV said Saniora and a number of leading figures in the March 14 Coalition, which opposes the Hezbollah-controlled 8 March Alliance, will issue a press statement about Friday's explosion in the coming hours.
A criminal evidence team from Lebanon's military police entered the Rafik Hariri hospital to examine Chatah's corpse, Future TV added.
Lebanese Prime Minister Najib Mikati denounced Chatah's assassination in a statement via Twitter, expressing hope that Lebanon would not suffer "more tragedies, devastation and harm."
"We condemn ex-minister Mohamed Chatah's killing, which targeted a political, academic and moderate person who had faith in dialogue, logic and the right to dissent," Mikati said.
Mikati revealed that he had had consultations with President Michel Suleiman over the killing and the required response.
British Foreign Secretary William Hague described the explosion as "sad news."
"My thoughts and sympathy with the people of Lebanon and the families of all those killed," Hague said on Twitter.
Saad Hariri posted a 280-word statement on his Facebook page.
"This is a new terrorist message for us," he said.
"Terrorists, killers and criminals are using car bombs, explosions and all other means to target Lebanon's free people one after another," Hariri added.
Chatah had "a mind full of ideas about the nation's peace, justice and well-being."
"Chatah is another branch falling from Rafik Hariri's tree", the Sunni leader asserted. "Those who assassinated Chatah are exactly those who assassinated Rafik Hariri, they seek to weaken and humiliate Lebanon."
Former Arab League secretary-general Amr Moussa announced his shock at Chatah's killing via a statement on Twitter.
"I mourn one of the best people I met in Lebanon. I offer my condolences to his family, his brotherhood and his beloved, as well everybody that knew him," he said.
Moussa added: I condemn this terrorist act and call on governments to prevent the Arab world becoming an arena of blood.
Lebanon has seen a wave of bombings over the past months as tensions rise over Syria's civil war.