At least five bombs exploded in two cities today, ripping through a government building and the offices of business groups and labor unions. Police said no injuries were reported. The early morning blasts went off simultaneously in Salonica and Athens, the capital. Police said anonymous callers claimed responsibility on behalf of the leftist guerrilla groups May 1 and the Revolutionary Popular Struggle. The groups have asked voters to boycott Sunday's crucial parliamentary elections, citing ``political mockery'' by the leading parties, the Conservatives and the Socialists. The Salonica blasts caused extensive damage at the European Community's northern Greece information center, located on the 6th floor of an office building, and the Industrialists Association of Northern Greece, police said. In Athens, bombs caused minor damage at the National Economy ministry, and buildings housing the General Confederation of Greek Trade Unions and the Federation of Greek Industrialists, they said on condition of anonymity. In the past, the attacks of the terrorist groups have focused on economic targets and none has ever caused fatalities. Both groups say they oppose capitalism, imperialism and the U.S. military presence in Greece. Greeks vote Sunday for the third time in a year, hoping to break a political deadlock that has created compromise governments unable to confront an economy in crisis and growing terrorism. But pollsters predict the election will end like those in June and November 1989, with no party winning enough seats to control the government.