ATHENS (Reuters) - A Greek anarchist group has claimed responsibility for a makeshift bomb that went off at a local courier company in Athens this week, smashing windows but causing no injuries.

Makeshift bomb and arson attacks have increased since Greece adopted deeply unpopular austerity measures in exchange for bailouts by the European Union and the International Monetary Fund for its debt-crippled economy.

The Informal Anarchist Federation-International Revolutionary Front (FAI-IRF) also claimed responsibility for an attack on Microsoft's Greek headquarters in June last year.

The blast on Sunday damaged some vehicles parked outside the firm and caused minor damage to several neighboring buildings. Police said the device consisted of at least five gas canisters and explosive material.

The courier company was also targeted in 2010 when the Greek guerrilla group Conspiracy of Fire Cells carried out parcel bomb attacks against embassies and foreign governments. Police have arrested dozens of suspected group members since November 2010.

"Nothing is over," the FAI-International Revolutionary Front said in a statement published on the Internet. "We've turned our promises for revenge to action."

Small scale attacks on businesses, police and politicians are frequent in Greece, with its long history of political violence.

Gas canisters detonated at the offices of Greece's deputy environment minister and two other ruling party lawmakers in the city of Thessaloniki on Tuesday, causing damage but no injuries.

(Reporting by Renee Maltezou; Editing by Mark Heinrich)