An explosion damaged a tax office near Athens early Tuesday, causing no injuries police said. The blast in the Argyroupoli area southeast of the city occurred at 2:30 a.m. and followed a warning telephone call to an Athens newspaper. Police had cordoned off the site before the blast and said they believed a bomb had been used. They said other details were not immediately available. The explosion occurred as authorities are battling a growing wave of arson attacks against banks and government offices by anarchist groups in Athens and Thessaloniki, Greece's second largest city. On January 12, assailants fired a rocket propelled grenade into the US Embassy building in central Athens, in an attack that caused no injuries and the government blamed on farleft Greek militants.