A government spokesman, Simos Kedikoglou, condemned the bombing. “The evident target of the attackers is to change this image, and change the agenda,” Mr. Kedikoglou said on a morning television news program. “We will not allow the attackers to achieve their aim.”

No one claimed responsibility, but two news outlets received warning calls shortly after 5 a.m. Some offices in the central bank were being used by representatives of Greece’s so-called troika of lenders, the International Monetary Fund, the European Commission and the European Central Bank.

The blast shattered windows, leaving intact only two wheels and the axle of the car. Militant groups in Greece have frequently set off bombs near symbolic targets or taken other steps to convey an antigovernment message.

Chancellor Angela Merkel of Germany, who more than any other leader in Europe is associated here with fiscal austerity, is scheduled to travel to Athens on Friday to meet with Prime Minister Antonis Samaras and is expected to affirm that the Greek government is on the right economic path.

Security around Ms. Merkel’s visit is expected to be tight, with the center of Athens locked down and helicopters patrolling.