A powerful explosion has been heard in southern Beirut and smoke was seen rising from the area, residents said.
There was no immediate word on damage or casualties caused by the blast in the Lebanese capital, which has been hit by a series of bombs in recent months.
Maged al-Maged, the head of the al-Qaeda-linked Abdullah Azzam Brigades, was reportedly detained by Lebanese troops in Beirut.
The embassy attack killed 23 people including the Iranian cultural attache on November 19.
Today's deadly explosion in Beirut interrupted a live interview on Lebanese TV station Future TV.
The explosion, which killed five people including a former minister, can be clearly heard inside the studio.
The British ambassador to Lebanon Tom Fletcher has paid tribute to the former Lebanese minister killed in a blast in Beirut and condemned his "cowardly assassination"
Residents have described seeing "panic and terror" in the streets of Beirut after a bomb blast hit the Lebanese capital killing five people including a former minister.
"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," Adel-Raouf Kneio said.
The blast, which was heard across the city at around 9:40 am local time, damaged restaurants, coffee shops and offices in downtown Beirut.
"I heard a huge explosion and saw a ball of fire and palls of black smoke. We run out of our offices to the streets," Hassan Akkawi, who works in a finance company nearby, said.
Witnesses described seeing glass everywhere, cars on fire and smelling explosives in the air.
Much of Beirut went into lockdown following the explosion, with police blocking off roads across the city.
A former Lebanese minister killed in a bomb blast in Beirut opposed Syrian president Bashar al-Assad and was a prominent critic of Lebanon's Shi'ite Hezbollah movement.
A tweet posted on his Twitter account less than an hour before the blast accused the Shi'ite movement of trying to take control of the country.
A Lebanon-based al Qaeda-linked group, the Abdullah Azzam Brigades, claimed responsibility for the attack and threatened further attacks unless Iran withdraws forces from Syria, where they have backed Assad's war against rebels.
Chatah was on his way to attend a meeting when the explosion tore through his car.
A Reuters witness at the scene said his car was "totally destroyed, it is a wreck", claiming they found Chatah's identity card, torn and charred inside his car.
The Foreign Secretary William Hague has said his thoughts and sympathies are with the people of Lebanon after a bomb blast rocked Beirut this morning.
At least five people, including a former Lebanese minister, are believed to have been killed when the explosion occurred in the downtown business district of the capital.
At least five people have been killed in Beirut, Lebanon, following an explosion, security sources said.
An explosion has hit the Lebanese capital Beirut, with the number of casualties currently unknown.
The blast was heard across the city and black smoke was seen rising near the Phoenicia Hotel.
Ambulances were seen taking victims from the area, according to a witness.
Former Lebananese minister Mohammed Shattah has been killed in a blast in Beirut, security sources have told Reuters.