The leader of Greece's Golden Dawn party has been arrested in a crackdown on the group launched after the murder of a leftist musician.
It is the first time since 1974 that sitting members of parliament have been arrested.
Two police officials said an operation by the counterterrorism unit is still ongoing, with a total of about 35 arrest warrants for Golden Dawn members issued. They spoke on condition of anonymity.
The arrests come 11 days after the killing of left-wing activist rapper Pavlos Fyssas 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 crackdown 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.
Mr Mihaloliakos warned on Friday that the party may pull its 18 politicians from parliament if the crackdown does not stop.
The move would prompt by-elections that could hurt the coalition government of Prime Minister Antonis Samaras, which has a slim majority of 155 MPs in the 300-seat parliament.
A formerly marginal organisation, Golden Dawn entered the Greek Parliament for the first time in May 2012, capitalising on Greece's deep financial crisis, rising crime and anti-immigrant sentiment, polling just under 7%. It has 18 deputies.
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.
Authorities also said they arrested a local Golden Dawn leader in an Athens suburb, as well as nine other unnamed party members.
In addition to Mr Michaloliakos and Mr 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.