ATHENS, Greece -- Police arrested the leader and other top officials of the extreme-right Golden Dawn party on Saturday 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 announced the arrests of 16 Golden Dawn members, including party head Nikos Michaloliakos, spokesman Ilias Kassidiaris and two other lawmakers. The arrests included a local Golden Dawn leader in an Athens suburb. The rest were ordinary members.

Two police officials said an operation by the counterterrorism unit was still ongoing late Saturday morning, with a total of about 35 arrest warrants for Golden Dawn members issued. They spoke on condition of anonymity because they were not permitted to speak publicly.

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." A small group of about 30 people initially gathered, standing on the sidewalk across the street from the building.

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.

In addition to Michaloliakos and Kassidiris, Golden Dawn deputy, Ilias Panayiotaros, gave himself up at police headquarters, telling police they were looking for him at a wrong address. Another lawmaker, Yannis Lagos, has also been arrested.

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  • AEK Athens midfielder Giorgos Katidis raises his hand in a Nazi style salute as he celebrates scoring the winner in a Greek league gaame against Veria in Athens' Olympic Stadium, Saturday, March 16, 2013. (AP Photo/INTIME)

  • Immigrants hold placards in Athens on December 15, 2012 during a European march for democracy against racism, antisemitism and neo-Nazism. (LOUISA GOULIAMAKI/AFP/Getty Images)

  • Members and supporters of the extreme right party Golden Dawn march in central Athens on Wednesday May 29, 2013, during a rally marking the anniversary of the fall of Constantinople to the Ottoman Empire in 1453. (AP Photo/Dimitri Messinis)

  • Athens mayor Giorgos Kaminis leaves on May 2, 2013 in Athens, after riot police had to use tear gas to disperse around 100 supporters of Greek neo-Nazi party Golden Dawn gathered in Syntagma square, below the parliament, for a food distrubition addressed strictly to Greeks. (ANGELOS TZORTZINIS/AFP/Getty Images)

  • Members and supporters of the extreme right party Golden Dawn march in front of the Greek Parliament in central Athens on Wednesday May 29, 2013, during a rally marking the anniversary of the fall of Constantinople to the Ottoman Empire in 1453. (AP Photo/Dimitri Messinis)

  • Members of the ultra nationalist party Golden Dawn chant the Greek national anthem outside the German embassy in Athens on March 22, 2013. (ARIS MESSINIS/AFP/Getty Images)

  • Members and supporters of the extreme right party Golden Dawn march in central Athens on Wednesday May 29, 2013, during a rally marking the anniversary of the fall of Constantinople to the Ottoman Empire in 1453. (AP Photo/Dimitri Messinis)

  • Ilias Panagiotaros, member of the Parliament of the extreme right party Golden Dawn gives orders to supporters in central Athens on Wednesday May 29, 2013, during a rally marking the anniversary of the fall of Constantinople to the Ottoman Empire in 1453. (AP Photo/Dimitri Messinis)

  • Panagiotis Iliopoulos, a deputy for the far-right Golden Dawn party, centre top, gestures as he shouts insults at other lawmakers with his colleague in the same party at the Greek Parliament in Athens, Friday, May 17, 2013. (AP Photo/Fosphotos, Panayiotis Tzamaros)

  • Supporters of the far-right party Golden Dawn sing the national anthem as they hold up flares and a sign which reads in Greek ''No to the anti-Greek policy of Germany'' during a protest outside the Germany embassy in Athens on Friday, March 22, 2013. (AP Photo/Thanassis Stavrakis)