BERLIN — Police were investigating a suspicious package at German Chancellor Angela Merkel's office Tuesday, hours after small mail bombs exploded outside the Russian and Swiss embassies in Athens in attacks blamed on far-left domestic extremistsGreek police destroyed at least three more suspected bombs in Athens.RELATED:Mail bomb found in Dubai traveled on two passenger planesNetanyahu: We stand before a rising wave of terrorNo group claimed responsibility for Tuesday's attacks, which caused no injuries. No warning was given. No link has been made with the recently discovered Yemen-based mail bomb plot, which used much more powerful devices.Greece has a vocal anarchist political fringe that opposes most forms of state authority — particularly the police and party democracy — and as well as capitalism and globalization.In recent decades, small radical anarchist or nihilist groups have staged attacks ranging from nighttime car burnings to bomb and gunfire attacks on symbols of state power and wealth — including the US embassy in Athens.Merkel was in Belgium when the package arrived in the mailroom of her office. Merkel's spokesman, Steffen Seibert, said that it showed "marks that indicated the possibility of explosives" and police were immediately alerted.Explosives experts continue to examine the package."It cannot be ruled out that the package contains explosives," Seibert said.The chancellory was not evacuated.Several German media outlets cited unspecified official sources as saying the package was personally addressed to Merkel and the Greek Economy Ministry was given as the return address. The reports could not immediately be independently confirmed.The attacks in Greece began Monday when a mail bomb addressed to the Mexican embassy exploded at a delivery service in central Athens, lightly wounding one worker.Authorities searched surrounding streets and arrested two suspects shortly after the blast. They were carrying mail bombs addressed to French President Nicolas Sarkozy and the Belgian Embassy, along with handguns and bullets in waist pouches. One wore body armor, a wig and a baseball cap.Police detonated the bombs along with a fourth device found at a delivery company and addressed to the Dutch Embassy. One of the suspects was wanted in connection with an investigation into a radical anarchist group known as Conspiracy Nuclei of Fire, which has claimed responsibility for a spate of small bomb and arson attacks over the past two years.The men were charged Tuesday with belonging to a terrorist group, acts of terrorism and causing explosions that endangered human lives. The charges carry a minimum 25-year prison sentence.The explosions in Greece continuedTuesday with the detonation of a bomb in the courtyard outside a six-story building that is home to the Swiss Embassy.Swiss Foreign Ministry official Georg Farago said Athens embassy employees regarded the package as suspicious after noticing "traces of metal" on it."The package burst into flames when the employees removed the external wrapping of the package. At the same moment, there was an explosion. No one was injured," Farago said.Soon after, a courier heading for another embassy became suspicious about a package and stopped at Parliament, where police explosives experts detonated a bomb.Police then found explosive devices at the Bulgarian Embassy and a central Athens courier company — where the German embassy had returned a suspicious package — and set them off in controlled explosions.A fifth bomb went off on the grounds of the Russian Embassy.Authorities closed down sections of the capital and checked dozens of potential targets, while all embassies were given additional police security.Sarkozy said his office took threat seriously and that French authorities were working with Greek police."The threat is very serious. We are extremely vigilant and I am following it very closely," Sarkozy said during a joint press conference in London with British Prime Minister David Cameron.