The Greek ministry of public works and environment was slightly damaged early Thursday after two separate blasts at its Athens headquarters and an annexe, police said. Two gas canisters exploded around 3:40 am (0140 GMT) in front of the ministry's main building near the city centre. Around half an hour later, two others went off at a nearby annexe. Five minutes after the first explosion, a hitherto unknown group calling itself the Revolutionary Organisation claimed responsibility in an anonymous call to a local radio station.