The former Lebanese Finance Minister Mohamad Chatah has been assassinated in a big bomb blast in central Beirut.
Four others were killed and at least 50 hurt in the suspected car bombing.
Mr Chatah, a Sunni Muslim, was an adviser to ex-PM Saad Hariri. He was also a staunch critic of Syrian President Bashar al-Assad and Lebanon’s Shia Hezbollah movement that backs him.
There has been a wave of attacks in Lebanon, linked to heightened Sunni-Shia tensions over the Syrian war.
Saad Hariri implicitly accused Hezbollah of carrying out the attack.
He blamed “those who are hiding from international justice and who have spread the regional fire to the [Lebanese] nation”.
Five Hezbollah suspects are due to go on trial in three week’ time, charged in connection with assassinating Saad Hariri’s father and former Prime Minister, Rafik, in a huge car bombing in February 2005.
Hezbollah has denied involvement in Rafik Hariri’s death.
No-one has claimed responsibility for Friday’s attack.
‘Terror and panic’
Mr Chatah was on his way to a meeting of the anti-Syrian March 14 bloc, led by Saad Hariri, when his convoy was hit.
The blast damaged several buildings near the Phoenicia Hotel and set several cars ablaze.
Witnesses described shock and fear at the scene of the blast.
“We were opening our store when we heard the blast. It was really loud. We are used to blasts in Lebanon but not in this area. Now we are not safe anywhere,” said Mohammad, a shop assistant quoted by AFP news agency.
Adel-Raouf Kneio, who saw the blast, told Reuters news agency the explosion “caught motorists driving in the morning rush hour” and “there was terror and panic among residents”.
“There was a big ball of fire and panic everywhere and then we learned that Chatah was the target,” he said.
In a Twitter message early on Friday, shortly before he was killed, Mr Chatah said Hezbollah was “pressing hard to be granted similar powers in security and foreign policy matters that Syria exercised in Lebanon for 15 years”.
Syria withdrew its forces from Lebanon amid a backlash over the killing of Rafik Hariri.
Hezbollah has sent fighters to help President Assad in the war against Sunni-led rebels in Syria. President Assad comes from the Alawite sect, a heterodox offshoot of Shia Islam.
Iran, which backs Hezbollah, saw its embassy in Beirut attacked last month. A little known Sunni militant group said it has carried out that attack.