Windows were smashed and desks and computers were damaged in the blast at the Administrative Reform Ministry building. A car was also damaged in the explosion.
"There was no warning call and the risk of someone being injured was big, as the building is centrally located," said a police official who declined to be named.
The bomb was made of at least five gas canisters, police said.
The ministry is tasked with reforming Greece's bloated public sector, a key demand by the country's international lenders.
The attack was the second in under a week. A similar bomb exploded at the office of former Prime Minister Costas Simitis on Tuesday last week.
Greece's coalition government, led by technocrat Prime Minister Lucas Papademos, denounced that attack as an attempt to destabilize the country ahead of national elections expected on May 6.
Gas canister attacks on police and businesses are frequent in Greece. Small bomb attacks against politicians have risen since the country adopted harsh austerity measures under the terms of two successive bailouts by the European Union and the International Monetary Fund.
(Reporting by Tatiana Fragou and John Kolesidis; Writing by Renee Maltezou; Editing by Karolina Tagaris)
Reuters
