The explosion of a homemade bomb rocked the Greek port of Piraeus this morning, damaging buildings and cars but causing no injuries, police said.

It was unclear whether the attack directed against ship repair company DT Marine, the latest in a string of bombings of businesses, was politically or criminally motivated.

"It may have been a criminal attack," a police official said on condition of anonymity. Greece's anti-terrorism squad was investigating the blast which damaged eight cars and three adjacent buildings.

There has been a string of bombing attacks against domestic and foreign businesses in Greece since widespread rioting in December sparked by the police killing of a teenager.