BEIRUT (AFP) - A little known Syrian rebel group has claimed responsibility for a car bomb attack that hit Hezbollah's stronghold in the southern suburbs of Beirut on Tuesday, wounding 53 people.

It also claimed it was behind an attack on a Hezbollah convoy in eastern Lebanon on June 28.

However the mainstream rebel Free Syrian Army condemned the attack in Beirut's mainly-Shiite southern suburbs, describing it as a "terrorist" act.

The group, named the Special Forces 313 Brigade, uses the black, red, green and white colours of the flag of the Syrian opposition, and Islamic terminology.

It describes itself as "an independent military formation, that fights in Syria for the victory of God's word".

"Special units from the 313 Brigade staged an attack using a car bomb on the Bir al-Abed area of the southern suburbs," the group said on its Facebook page.

"We warned again and again against (Hezbollah's) intervention in Syria," the brigade added.

It cited "the failure of Lebanese politicians to control" Shiite militant group Hezbollah movement as one of the reasons for the attack.

Hezbollah fighters publicly intervened in the conflict in neighbouring Syria in April, siding with President Bashar al-Assad's regime against the mainly Sunni rebels.

The rebel group said a massive offensive against rebel-held areas of the central city of Homs was being waged "with the participation of the mercenaries of (Hezbollah chief) Hassan Nasrallah".

The Bir al-Abed car bomb attack, which wounded 53 people, was the most serious incident in Hezbollah's Beirut stronghold since the start of the Syria war more than two years ago.

"This attack was not the first and it will not be the last, and (Hezbollah) knows full well who targeted its soldiers in the Ksara area of Zahle (in eastern Lebanon) last month," said the 313 Brigade's statement.

On June 28, two small explosive devices went off in Zahle targeting a Hezbollah convoy.

"We will chase down any remnants of this terrorist group, wherever they may be, until they stop taking part in the bloodletting of the Syrian people," the 313 Brigade warned.

The mainstream rebel FSA condemned the bombing.

"The position of the FSA supreme command is clear - we condemn this as a terrorist attack that targeted civilians, and do not consider it a military operation," its political and media coordinator, Louay Muqdad, said.