Athens  - A strong explosion shook central Athens after a bomb went off Thursday on a busy avenue, causing damage to a government building but no injuries, the state news agency said.

The explosive device went off outside the building of the State Property Company, a short distance from Athens' central police headquarters and Greece's supreme court, damaging nearby cars and buildings.

Police cordoned off the area, one of the busiest avenues in Athens.

There was no warning prior to the explosion and no group claimed responsibility for it, but officials suspect leftist militant groups to be behind the attack.

Greece has been plagued by daily bombings and arson attacks on banks and multinational businesses since the shooting of a teenager in December, which sparked the worst riots the country has seen in decades.

Experts fear that the militant group Revolutionary Struggle, which recently claimed responsibility for bomb attacks on two Citibank branches, and the new Sect of Revolutionaries have recruited fresh members since those riots and have acquired large quantities of arms and explosives.

Revolutionary Struggle has claimed responsibility for a number of attacks against government offices and police, including a rocket attack against the US embassy in Athens in 2007.

The violence has embarrassed Prime Minister Costas Karamanlis' government, which has been criticized for its inability to protect citizens.

Earlier this week, the government vowed to crackdown on the increasing violence and has sought advice from Scotland Yard. (dpa)