Former Lebanese minister Mohamad Chatah, who opposed Syrian President Bashar al-Assad, was killed in a massive bomb blast on Friday which one of his political allies blamed on the Shi'ite Hezbollah militia.

Friday's attack also killed five other people and threw Lebanon, which has been drawn into neighbouring Syria's conflict, into further turmoil after a series of sectarian bombings aimed at Shi'ite and Sunni Muslims over the past year.

Former prime minister Saad al-Hariri accused Hezbollah of involvement in the killing of Chatah, his 62-year-old political adviser, saying it was "a new message of terrorism."

"As far as we are concerned the suspects ... are those who are fleeing international justice and refusing to represent themselves before the international tribunal," Hariri said.

Chatah's killing occurred three weeks before the long-delayed opening of a trial of five Hezbollah suspects indicted for the 2005 bombing which killed former prime minister Rafik al-Hariri, Saad's father, and 21 other people.

The trial is due to open in The Hague in January. The suspects are all fugitives and Hezbollah, which denies any role in the Hariri assassination, has refused to cooperate with the court, which it says is politically motivated. Preliminary U.N. investigations implicated Syrian officials.

Lebanese security men, center, detain a man for inquiry at the scene of an explosion in central Beirut, Lebanon, Friday. (Hussein Malla/Associated Press) Hezbollah, which has sent fighters to Syria to help Assad's forces against rebels in the civil war, condemned Friday's blast as a "horrible crime."

The explosion destroyed Chatah's car, turning it into a heap of twisted metal, and injured another 71 people. It took place not far from where Rafik al-Hariri, a former prime minister and influential Sunni figure, was assassinated by a huge bomb in February 2005.

The attack on Chatah is linked to a power struggle that has raged in Lebanon since Hariri's assassination. This was followed by a series of attacks which killed anti-Syrian politicians, officials and journalists. In October last year, General Wissam al-Hassan, an intelligence chief linked to Hariri, was killed by a car bomb in Beirut.

Chatah, a vocal critic of Hezbollah, was regarded as one of the brains behind the Hariri-led Future movement and March 14 opposition coalition, and their point person with Western governments.

A message on Chatah's Twitter account less than an hour before the blast accused Hezbollah of trying to take control of the country, which was occupied by Syrian forces until after Hariri's assassination.

"Hezbollah is pressing hard to be granted similar powers in security and foreign policy matters that Syria exercised in Lebanon for 15 years," the tweet read.

The conflict in Syria has polarised Lebanon and increased sectarian tensions. Hezbollah members are fighting for Assad — who is from the Alawite sect, an offshoot of Shi'ite Islam — while some of the Sunni Syrian rebel groups are linked to al Qaeda, which is also seeking to topple Assad.

Former minister Marwan Hamadeh, who survived a car bomb in 2004, told Al Arabiya television: "Hezbollah will not be able to rule Lebanon, no matter how much destruction it causes or blood it spills."

Hezbollah condemned the blast as "part of a series of crimes and explosions aimed at destablizing the country and its unity" in a statement issued before Hariri had accused it of involvement.

Attack condemned

Lebanese President Michel Suleiman and Prime Minister Najib Mikati and officials from across Lebanon's sectarian political divide condemned Chatah's killing.

'For a while I was thinking, 'Am I still alive?' I didn't know what happened. I was just seeing the people running and holding their ears and eyes, and running. - Dress shop manager Maya.

Mikati said the blast targeted "a moderate academic and noble political figure who believed in dialogue, the language of reason and the right to different views."

Fouad Siniora, a leading member of the March 14 opposition movement to which Chatah belonged, said the latest killing would be referred to the Special Tribunal.

"The killer is the same one that has been targeting the heroes of Lebanon. The crime occurred... weeks before the opening of the Tribunal in the Hariri assassination," he said.

While Chatah had no political power base of his own, his international experience, diplomatic contacts and academic analysis made him a leading member of Hariri's circle of advisers.

An economist and a diplomat, he worked for the International Monetary Fund in Washington and served as Lebanon's ambassador to the United States. He was also minister of finance from July 2008 to November 2009, after which he worked as a foreign policy adviser to the younger Hariri.

Sources at the explosion site said Chatah was on his way to attend a meeting at Hariri's headquarters when the explosion tore through his car. Hariri himself has stayed away from Lebanon for more than two years, fearing for his safety.

Investigators said the blast was caused by a 60-kilogram bomb.

A Reuters witness said Chatah's car was "totally destroyed, it is a wreck." Chatah's identity card, torn and charred, was found at the scene.

Iran, which backs Hezbollah, came under attack in Beirut last month. On Nov. 19, two suicide bombings rocked its embassy compound, killing at least 25 people including an Iranian cultural attache.

The sound of Friday's blast was heard across the city at around 9:40 a.m. local time and black smoke was seen rising in the chic downtown business and hotel district. It shattered glass in nearby apartment blocks and damaged cars, restaurants, coffee shops and offices.

"I heard a huge explosion and saw a ball of fire and palls of black smoke. We ran out of our offices to the streets," said Hassan Akkawi, who works in a finance company nearby.

"The explosion caught motorists driving in the morning rush hour here. 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," said Adel-Raouf Kneio.

Much of Beirut went into lockdown following the explosion, with police blocking off roads across the city.

After a series of explosions in the capital and in the northern city of Tripoli, the Lebanese army had stepped up security measures ahead of Christmas and New Year, fearing further attacks.

Fear and panic

The explosion shocked residents and emptied the streets in downtown Beirut, where people seeking a respite from recent turmoil had ventured out to enjoy the Christmas and New Year holiday period.

An explosion in Beirut, Lebanon on Friday sent black smoke billowing from the centre of the capital city. The blast went off a few hundred metres from the government headquarters and parliament building. (Bilal Hussein/The Associated Press) "I was on my way to open the store and then the explosion happened. For a while I was thinking, 'Am I still alive?' I didn't know what happened. I was just seeing the people running and holding their ears and eyes, and running," said Maya, manager of the Taten dress shop.

The owner of a restaurant down the street from the blast site, whose windows were smashed, said: "The damage to the glass is not the problem. People won't want to come here now. We were fully booked for the next five days."

Workers at luxury dress shops next to the site, where the entire glass facade was destroyed, were sweeping up glass, picking up damaged mannequins and counting the damage to the luxury dresses.

"I consider all this terrorism, damaging the country and the people. What can we say more? God helps us, God help this country," said Lebanese citizen Jamal near the explosion scene.