Police have arrested the leader of Greece's extreme-right Golden Dawn party and other top members on charges of forming a criminal organisation.
It is the first time since 1974 that sitting members of Parliament have been arrested.
Police announced the arrests of 16 Golden Dawn members, including party head Nikos Michaloliakos, the group's spokesman and three other lawmakers.
An operation by the counter-terrorism unit was still ongoing on Saturday, with a total of 35 arrest warrants for Golden Dawn members issued, two police officials said.
The government ordered an investigation into Golden Dawn's activities after the death of rapper Pavlos Fyssas on September 18.
A police officer was also arrested on Saturday.
The case is being handled by Greece's Supreme Court and anti-terrorist squad under organised crime laws.
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% of the vote in general elections last year.
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 group of about 100 people, including several deputies, gathered, standing on the pavement across the street from the building.
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.