A top Lebanese security official is among eight people killed by a car bomb in the country's capital Beirut.
Wissam al Hassan died in the rush-hour bomb in the city's east - which also wounded some 80 people - heightening fears that the Syrian civil war is spilling over into Lebanon.
Al Hassan's investigations had implicated Syria and Hizbollah in the assassination of former Lebanese prime minister Rafiq Hariri seven years ago.
He had also uncovered a recent bomb plot that led to the arrest of a pro-Syrian Lebanese politician, according to a Lebanese official.
He was a close aide to Hariri, a Sunni Muslim who was killed in a 2005 bomb attack in downtown Beirut.
Friday's bombing was the city's first major car bomb attack since 2008.
Lebanon's state-run National News Agency said the blast, in the mainly Christian east Beirut, took place only 200 yards from the headquarters of the Christian party, the Phalange.
A wounded woman near the site of the explosion The party is hostile to the regime of President Bashar al Assad in neighbouring Syria, which is mired in a lengthy civil war.
But Syrian information minister Omran al Zoabie told reporters: "We condemn this terrorist explosion and all these explosions wherever they happen. Nothing justifies them."
Michael Fish, 25, a British musician visiting Beirut, said he was in his hotel a street away when the explosion happened.
"At first I thought it was an earthquake," he said.
"It shook the whole hotel for a second. I ran down and started filming on my iPhone."
The AFP news agency reported that two apartment buildings had been devastated by the bombing in a narrow street off Sassine Square in Ashrafieh. One building was still on fire as Red Cross workers evacuated bloodied casualties.
Balconies were torn off by the force of the blast, windows shattered and cars crushed by falling masonry.
Phalange leader Sami al Gemayel, a staunch opponent of Mr Assad and a member of parliament, condemned the attack.
"Let the state protect the citizens," he said.
"We will not accept any procrastination in this matter, we cannot continue like that. We have been warning for a year. Enough."
The war in Syria, which has killed 30,000 people in the past 19 months, has pitted mostly Sunni insurgents against Mr Assad, who is from the Alawite sect linked to Shi'ite Islam.
Interior minister Marwan Sharbel was also at the scene of the bombing. The previous such attack in Beirut, in January 2008, killed Lebanon's top anti-terrorism investigator and three other people.
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