Greek police have arrested the leader of the far-right Golden Dawn party, Nikolaos Michaloliakos, on charges of forming a criminal organisation.
Three more Golden Dawn MPs, a party leader in an Athens suburb and 12 other people have also been arrested.
The arrests come amid anger over the murder on 18 September of anti-racist musician, Pavlos Fyssas.
A man held for the stabbing told police he was a Golden Dawn supporter, though the party strongly denies any link.
Not since the end of Greece’s military dictatorship in 1974 has there been a mass arrest of MPs. It is an extraordinary clampdown by a government long accused of taking a soft touch towards Golden Dawn.
Some 154 racist attacks were recorded here last year and 104 so far this year – most attributed to Golden Dawn members. Two immigrants have been killed, again blamed on the party. But only now, after the killing of the hip hop artist Pavlos Fyssas, have authorities moved in hard and fast.
The government says it is this crime that has definitively exposed a direct chain of command to the party leadership, providing the basis for Golden Dawn to be classified as a criminal group.
The party has already had the immunity provided for Greek MPs lifted and one of those arrested on Saturday was tried earlier in the year in a separate incident. But with these arrests and several suspensions of police officers accused of links to Golden Dawn, the government has done more against the party this week than it has in the past year.
One of the MPs arrested on Saturday was party spokesman Ilias Kasidiaris.
Another, Ilias Panayiotaros, told reporters before giving himself up: “Shame on them, the people will lift Golden Dawn higher.”
A number of other warrants are believed to have been issued. The arrests were made by the anti-terrorism unit.
Golden Dawn has called on its supporters to rally outside the police headquarters in Athens and has vowed to fight back.
A text message read: “We call upon everyone to support our moral and just struggle against the corrupt system!”
Some 200 Golden Dawn members later rallied at the police HQ in the capital.
The killing of Pavlos Fyssas, 34 – whose stage name was Killah P – has sparked protests in Athens and across Greece.
George Roupakias, 45, who said he was a supporter of Golden Dawn, was arrested. He was charged with voluntary manslaughter and illegal possession of a weapon.
The government launched a crackdown, including raids on Golden Dawn premises.
Two senior police officials resigned for “personal reasons” after the killing and another two were suspended. Seven other police officers were suspended.
The government also began an inquiry into the activities of Golden Dawn, which won nearly 7% of the vote in 2012 elections.
Prime Minister Antonis Samaras has vowed not to let the party “undermine” democracy, and government officials say it must now be treated as a “criminal organisation”.
Golden Dawn, Greece’s third most popular party, has accused the government of carrying out a witch-hunt over the Fyssas killing.
Mr Michaloliakos, 56, said last week: “We will exhaust any means within our legal constitutional rights to defend our political honour. If the country enters a cycle of instability, it is those who demonise Golden Dawn who will be responsible.”
On Friday, Golden Dawn threatened to pull its 18 MPs out of the 300-strong Hellenic Parliament.
Mr Samaras’s coalition, which has 155 seats, would then face by-elections.
On Saturday, Mr Samaras ruled out the possibility of early elections, adding that the Golden Dawn case was “now in the hands of the justice system”.
In recent months, Golden Dawn has been accused of perpetrating attacks on migrants and political opponents – including an attack on Communist Party members earlier this month which is said to have left nine people in hospital.
Golden Dawn officially denies being a neo-Nazi movement, though its badge resembles a swastika, some senior members have praised Adolf Hitler, and its members wear black T-shirts and combat trousers at anti-immigrant demonstrations.
BBC © 2013