Senior leaders of the neo-Nazi Golden Dawn were ordered to immediately begin their prison sentences by a Greek court, capping one of the most significant trials in the country's political history.
After the ruling, arrest warrants were issued for Golden Dawn's leader Nikos Michaloliakos and senior aides.
Michaloliakos and other former members of his inner circle were sentenced two weeks ago to more than 13 years in prison for running a criminal organisation after a five-year trial.
Michaloliakos, a long-term Hitler admirer and Holocaust denier, has described his party's prosecution as a political witch hunt.
He remained defiant on Thursday after the court ordered his imprisonment.
"I'm proud to be taken to jail for my ideas … we will be vindicated by history and by the Greek people," he told reporters outside his home in an affluent northern Athens suburb.
"I thank the hundreds of thousands of Greeks who stood by Golden Dawn all these years," said the 62-year-old mathematician and former protégé of Greek dictator Georgios Papadopoulos.
Those going to jail include deputy Golden Dawn leader Christos Pappas and the party's former spokesman Ilias Kassidiaris, who recently formed a new nationalist party.
But the ruling cannot be immediately enforced in the case of former Golden Dawn lawmaker Ioannis Lagos, who was elected to the European parliament in 2019 and has immunity.
Greek judicial authorities must formally request that Lagos' immunity be lifted by the European parliament before he can be imprisoned.
The court had issued guilty verdicts to Michaloliakos and more than 50 other defendants, including his wife, on October 7.
But any conclusion was delayed by a number of legal disputes, including last week when Lagos tried to have the court's three judges recused, on account of perceived bias.
Head judge Maria Lepenioti on Monday publicly questioned the state prosecutor's demand that most of the convicted be provisionally released pending appeal trials, which could take years to adjudicate.
The court has accepted that Golden Dawn was a criminal organisation run by Michaloliakos using a military-style hierarchy modelled on Hitler's Nazi party.
The probe was sparked by the 2013 murder of anti-fascist rapper Pavlos Fyssas, who was ambushed by Golden Dawn members and fatally stabbed.
Mr Fyssas' murderer, former truck driver Yiorgos Roupakias, has been handed a life sentence.
In a lengthy investigation, pre-trial magistrates outlined how the group formed a black-clad militia to intimidate and beat up opponents with knuckle dusters, crowbars and knives.
A search of party members' homes in 2013 uncovered firearms and other weapons, as well as Nazi memorabilia.
Another former Golden Dawn organiser, former death metal bassist Georgios Germenis, who is now an assistant for Lagos at the European parliament, said on Thursday that his conviction was "absurd" and politically motivated.
"I am 100 per cent innocent. I was just helping people," Germenis said as he turned himself in at his local police station.
For Michaloliakos, the sentence caps a stunning downfall for a man whose party was the country's third most popular in 2015, the year the trial began.
The party won 18 seats in parliament in 2012 after tapping into anti-austerity and anti-migrant anger during Greece's decade-long debt crisis.
It failed to win a single seat, however, in last year's parliamentary election.
Michaloliakos and other former Golden Dawn lawmakers had already spent several months in prison after Mr Fyssas' murder in 2013.
Time served in pre-trial detention will be deducted from the overall sentence.
Under Greek law, they must serve at least two-fifths of their sentence before even requesting an early release.