Greek police arrested the leader, two lawmakers and party members from the far-right Golden Dawn party on Saturday, and charged one member with being an accomplice to the killing of an anti-fascist rapper, a police official said.
Police said party leader Nikolaos Mihaloliakos, spokesman Ilias Kasidiaris, two other lawmakers and 10 members had been arrested on charges of founding a criminal organization. They are due to appear in court this weekend to be formally charged.
Golden Dawn, ranked Greece's third most popular party in opinion polls, is under investigation for the murder of Pavlos Fissas which sparked violent protests and a crackdown on political extremism.
(Read more: Greek policeraid Golden Dawn after stabbing)
The party has denied any links to the killing and Mihaloliakos has warned the party could pull its 18 lawmakers from parliament if the crackdown does not stop.
If potential by-elections were won by the opposition, as some polls indicate, Greece's fragile two-party coalition would become politically untenable, Mihaloliakos has argued.