The leader of Greece’s extreme-right Golden Dawn party and four more of its leaders in Parliament were arrested and charged Saturday with forming a criminal organization — the latest episode in a rapidly widening campaign by the government to clamp down on what it says is a rising tide of extremism in Greece, fueled by a devastating economic crisis.

Counterterrorism police arrested Golden Dawn leader Nikos Michaloliakos, party spokesman Ilias Kassidiaris and Yannis Lagos, Nikos Michos and Ilias Panayiotaros. The last two gave themselves up voluntarily. A sixth parliamentarian, Christos Pappas — described in a prosecutor’s report as the Golden Dawn’s No. 2 — remains at large.

It was the first time since the fall of a military junta in 1974 that sitting members of Parliament have been arrested.

An additional 15 people, including 13 Golden Dawn members and two police officers, have also been arrested and are due to appear before a prosecutor and an examining magistrate soon. They face the same charges.

A police official said a total of 38 warrants had been issued and the counterterrorism unit was still searching for 18 of them, including the missing deputy.

“It is an unprecedentedly dynamic response to a neo-Nazi organization,” government spokesman Simos Kedikoglou said, hinting the arrests were the culmination of a long strategy to deal with Golden Dawn as a criminal, not a political force.

“The prime minister and the government were determined to deal with Golden Dawn solely through the justice system … We have succeeded in stripping them of their political cover and deal with them as what they really are, a criminal organization,” Kedikoglou said.

The arrests underline the Greek government’s efforts to stifle the fiercely anti-immigrant party, which has been increasingly on the defensive since the killing of an anti-fascist Greek musician a week and a half ago.

Pavlos Fyssas, a 34-year-old rapper whose lyrics protested the rise of neo-fascism in the country, was killed on Sept. 18, sparking outrage across Greece. The suspect arrested over his death admitted to police that he had stabbed the man and identified himself as a supporter of Golden Dawn. Police investigated his cellphone records and those of more than 300 people connected to Golden Dawn.

Investigations have even extended to the police, which have been accused in the past of turning a blind eye to Golden Dawn violence and of mistreating immigrants.

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

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 party has vehemently denied any role in the killing, but it has appeared to dent Golden Dawn’s appeal among Greeks. As calls for a crackdown mounted, the party hinted its parliamentarians might resign to provoke elections in 15 multi-party constituencies.

Golden Dawn is by no means a new force in Greece, but its influence has grown in tandem with the country’s devastating economic hardship. Offering promises to restore jobs and order, the party’s members also espouse nationalistic and xenophobic stances, appealing to marginalized Greeks in rough areas populated by a rising number of unemployed immigrants, mostly from Pakistan and North Africa.

Human rights groups say Golden Dawn, whose members perform Nazi salutes at rallies and meetings, has systematically terrorized immigrants, while the police have looked the other way. The aggressive acts include the beating of immigrants with clubs and shields bearing swastikalike symbols, or with wooden poles draped in the Greek flag.