The death toll in the car bomb blast in a Hezbollah stronghold in a suburb of the Lebanese capital Beirut has risen to 21 and it is feared the casualty figure could go up further. Some of the 25 injured are reported to be in critical condition in hospitals.

Although local reports suggest it was a suicide bomber who triggered the explosion inside a car, the cause of the blast is still unclear.

An unknown Sunni insurgent group which calls itself Brigades of Aisha claimed responsibility for the explosion targeting the Shiite-oriented Islamist militant outfit, Hezbollah.

The blast, which took place at Ruwaiss when scores of people were returning from work, wrecked several buildings in the locality and many vehicles were engulfed in flames.

In a message directed at Hezbollah leader Hassan Nasrallah, the Brigades of Aisha said: "We ... send a message to Hassan Nasrallah's pigs. This is the second time that we decide the place of the battle and its timing...And you will see more, God willing."

Meanwhile, Lebanese officials blamed Israel for the attack saying it bears the mark of Israel-style attacks.

"The terror attack was planned well. It could be connected to the wounding of the Israeli soldiers in al-Labouneh in southern Lebanon," said Lebanese interior minister Marwan Charbel.

The Hezbollah-owned Al-Manar television in Lebanon said: "Terrorism has struck the southern suburbs again," adding that the outfit is "paying the price for its position".

The attack is the latest in a series of Shiite-Sunni clashes in Lebanon fuelled by the conflict in neighbouring Syria.

The Syrian regime in Damascus has condemned the attack calling it "a coward act in the service of the Israeli enemy".

Syria's Information Minister Omran al-Zoubi said in a statement: "Syria strongly condemns that terrorist act and offers condolences to the families of victims and hopes quick recovery for the wounded."

People gather around the site of an explosion in Beirut's southern suburbsReuters
Supporters of Hezbollah try to extinguish the fire from burning cars at the site of a car bomb in Beirut's southern suburbsReuters
A Supporter of Hezbollah gestures as he stands at the site of a car bomb in Beirut's southern suburbsReuters
Hezbollah supporters react as they try to extinguish a fire at the site of an explosion in Beirut's southern suburbsReuters
People escape from a burning building near the site of an explosion in Beirut's southern suburbsReuters
Civilians carry a wounded man on a stretcher at the site of an explosion in Beirut's southern suburbsReuters