Five top officers have been replaced after Greece ordered urgent inquiries into alleged links between the far-right Golden Dawn party and the country's police and military.
The Public Order Ministry said the heads of the police's special forces, internal security, organised crime, firearms and explosives, and a rapid-response motorcycle division had been moved to other posts pending an investigation into weekend media reports that police gave the party with assistance in alleged criminal activity.
Golden Dawn won nearly 7% of the vote in general elections last year, but is currently the subject of a criminal investigation following the murder last week of an anti-fascist rapper.
The party angrily denies any involvement in the murder of Pavlos Fyssas. A 45-year-old man, who authorities say has identified himself as a Golden Dawn volunteer, has been arrested for the murder and is in police custody.
The government is seeking the prosecution of members of the far-right party under the country's anti-terrorism law and is preparing a parliamentary amendment that would see Golden Dawn's state campaign funding suspended if its MPs are accused of serious offences. It describes the party as neo-Nazi and says it is behind a growing number of brutal street attacks against mostly Asian immigrants by far-right gangs.
The action against the officers was taken to "to ensure the absolute objectivity" of the police inquiry, the government said. Two less senior officers were also replaced and a third was suspended, while regional police commanders of southern and central Greece resigned, citing personal reasons.
Separately, the Defence Ministry has ordered its own inquiry into the news reports that Golden Dawn members were receiving informal training from serving and reservist special forces officers in the Greek military.
Nikos Michaloliakos, the Golden Dawn leader, described the claims of paramilitary training and the government allegations linking his party to Mr Fyssas' murder as "monstrous lies". "We are under an all-out and dirty attack from a system that is rotten," he said on a live webcast streamed on the party's internet site. "I am supposed to prove that I am not a criminal, not the mafia. But my question is: is there any bigger criminal gang than those in power, who led the country to bankruptcy and handed over our national sovereignty?"
Golden Dawn, whose leaders have previously expressed admiration for Adolf Hitler and use openly racist rhetoric against non-European immigrants, has seen a surge in support over the past two years as the country struggled through harsh economic crisis.
Its popularity in opinion polls has risen further since the last election in June 2012 - alarming mainstream political parties faced with regional and European Parliament elections next year. A survey in the conservative Eleftheros Typos newspaper found a sharp dip in support for Golden Dawn over the past week, from 8.3 to 5.8%, with other parties broadly unchanged.