Police have arrested the leader and other top officials of the extreme-right Golden Dawn party on charges of forming a criminal organization, in an escalation of a government crackdown after a fatal stabbing allegedly committed by a supporter.

It is the first time since 1974 that a party head and sitting members of Parliament have been arrested.

Police on Saturday announced the arrests of party head Nikos Michaloliakos, spokesman Ilias Kassidiaris, as well as deputies Ilias Panagiotaros and Ioannis Lagos. Authorities also said they arrested the general secretary of Golden Dawn's Nikea chapter Nikos Patelis, as well as nine other unnamed party members.

Skai reported that two police officers were also arrested during the operation by the counterterrorism unit that is still ongoing, with more than 30 arrest warrants for Golden Dawn members issued.

Justice Minister Haralambos Athanasiou and Public Order Minister Nikos Dendias met with Greek Prime Minister Antonis Samaras to brief him on developments.

Despite the arrests, the party's lawmakers retain their parliamentary seats unless they are convicted of a crime. Golden Dawn holds 18 of Parliament's 300 seats, after winning nearly 7 percent of the vote in general elections last year.

The arrests come 11 days after the killing of a left-wing activist rapper by an alleged Golden Dawn member. Though the party has vehemently denied any role in the killing, it has appeared to dent its appeal among Greeks and the government has worked to crack down on the party.

Golden Dawn expressed outrage at the arrests in a text message to journalists. "We call upon everyone to support our moral and just struggle against the corrupt system! Everyone come to our offices!," it said.

A later text message called for supporters to head to police headquarters "with calm and order." Hundreds of Golden Dawn sympathizers have reportedly gathered outside the building chanting slogans in support of the party.

“You dismantled the police and EYP (the National Intelligence Service) in order to arrest us,” Giorgos Germenis told journalists gathered at the site.

A formerly marginal organization with neo-Nazi roots, Golden Dawn entered the Greek Parliament for the first time in May 2012, capitalizing on Greece's deep financial crisis, rising crime and anti-immigrant sentiment.

The party's members and supporters have frequently been suspected of carrying out violent attacks, mainly against immigrants. Despite its reputation for violence, the party had enjoyed growing popularity.

A government spokesman refused to comment on the details of the operation.

"Democracy can protect itself. Justice will do its job," Simos Kedikoglou told reporters.

Dimitris Papadimoulis, parliamentary spokesman for leftist SYRIZA opposition, said that the country's legal arsenal was enough to crack down on any criminal acts committed by members of Golden Dawn.

“It is crucial to substantiate these charges,” he told Skai ahead of a party meeting to discuss the latest developments.

In a statement on Saturday, the European Commission expressed its “full confidence in the Greek justice to take all necessary actions, in respect of legal procedures."

“The Greek political system has risen to the challenge and [is taking steps to] protect the democratic rule of law," EU Commissioner Maria Damanaki told Kathimerini in Brussels.

[AP, Kathimerini English Edition]