Assailants raked the German ambassador's residence in Athens with gunfire early on Monday in an attack that caused no injuries, Greek police officials said.

The police found 60 spent bullet casings at the scene and detained six people in connection with the incident, which occurred around 3:30 a.m. in an affluent suburb north of Athens. The bullet casings came from two Kalashnikov assault rifles, according to the police.

No one claimed responsibility for the attack, in which four bullets hit a security gate. But anti-German sentiment has been festering among many Greeks struggling with record unemployment and reduced salaries under a harsh austerity plan required for Greece's international bailout, which Germany had a major role in selecting the terms of.

"The Greek government expresses its abhorrence and utter condemnation of today's cowardly act of terrorism, the sole and obvious target of which was Greece's image abroad just a few days before the start of the Hellenic Presidency of the Council of the E.U.," the Greek Foreign Ministry said in a statement.

Germany is the largest contributor to Greece's 240 billion euro, or roughly $330 billion, bailout. Recently, Prime Minister Antonis Samaras has publicly been pressing Germany to reduce and renegotiate Athens' delinquent debts as it grapples with a wrenching five-year recession — something Germany has refused to do.

That has also fed a persistent low-grade anger over hundreds of billions of euros in reparations that Greeks say Germany owes the country from World War II, money that some say should go toward helping to forgive Greece's debt bill. Greek newspapers regularly run articles on how much money Germany owes Greece.

Greece, which on Wednesday will take over the rotating European Union presidency for six months, has made some progress in improving its finances to meet the terms of the bailout — so much so that it is forecast to have a primary surplus before debt payments in 2014 for the first time in five years. But Greece still faces a mountain of debt that economists say is all but unpayable unless some new form of debt forgiveness is extended to Athens.

Over the weekend, Jens Weidmann, the chairman of the German Bundesbank and a member of the European Central Bank's Governing Council, ruled out another reduction in Greece's state debt, saying in a German newspaper interview that Athens still needed to press ahead with a number of reforms as required by the terms of its bailout.

While financial markets have calmed recently, he told the newspaper Bild, "this could be some misleading safety. The crisis could be fanned again like a fire."

His remarks echoed those of the German finance minister, Wolfgang Schäuble, who is widely reviled in Greece. During a visit to Athens this summer, police locked down the center of the city to pedestrian and car traffic as helicopters flew overhead, leaving the streets in a ghostly state of quiet. The scenes were reminiscent of when Chancellor Angela Merkel visited Greece in 2012.

Representatives of the so-called troika of lenders — the European Central Bank, the International Monetary Fund and the European Commission — are scheduled to return to Athens in January to resume talks over a fresh 4.9 billion euro tranche of aid.

Mr. Samaras telephoned Ms. Merkel after the attack and the Foreign Minister Evangelos Venizelos spoke by telephone with the German ambassador, Wolfgang Dold, and with his German counterpart, Frank-Walter Steinmeier.

The same building was targeted in a rocket attack in May 1999 claimed by the terrorist group November 17, which has since been dismantled.

Although no group has claimed responsibility for the attack on Monday, the incident follows an apparent rise in violent incidents both by far-right and far-left groups in Greece.