The leader of Greece's neonazi Golden Dawn party and four other of its MPs have been formally charged with membership of a criminal organisation with intent to commit crimes.

It was the first time since 1974 that sitting members of the Greek parliament had been arrested.

Golden Dawn leader Nikos Michaloliakos, party spokesman Ilias Kassidiaris and MPs Yannis Lagos, Nikos Michos and Ilias Panayiotaros were arrested by counter-terrorism police.

A sixth MP, Christos Pappas, remains at large.

A further 15 people, including 13 Golden Dawn members and two police officers, have also been arrested and are due to appear before an examining magistrate facing the same charges.

A police spokesman said that the counter-terrorism unit was still searching for 12 suspects, including the missing MP.

"It is an unprecedentedly dynamic response to a neonazi organisation," said government spokesman Simos Kedikoglou.

"We have succeeded in stripping them of their political cover and will deal with them as what they really are, a criminal organisation," Mr Kedikoglou said.

Citizen Protection Minister Nikos Dendias compared Golden Dawn members to German SS squads.

"The state has proven that it is not helpless in the face of organised violence," he said.

"Greek society will not tolerate any stormtroopers," Mr Dendias added.

Investigations have included the police force, which has been accused in the past of turning a blind eye to Golden Dawn violence.

Under existing anti-terrorism legislation, membership of a criminal organisation is a crime for which Golden Dawn deputies can be prosecuted without the parliament needing to lift their immunity.

There is no provision in the Greek constitution for the banning of a political party on the grounds of ideology, which is why the government has documented a series of criminal acts.

The prosecutor's report says that the people under arrest and those still at large were responsible for murders, violent attacks, explosions and extortion.

"We are rejoicing that the anti-fascist and anti-racist movement has forced the prime minister to make these arrests," said human rights group Keerfa, adding that politicians have "for too long protected the action of neonazis."