ATHENS, Greece (JTA) — A Greek court ordered the head of the ultranationalist Golden Dawn party held in jail until his trial.

Party leader Nikolaos Michaloliakos was arrested last week with several other lawmakers and senior Golden Dawn members on charges of forming a criminal organization, part of an unprecedented crackdown on the neo-Nazi party.

The judge made the decision to incarcerate Michaloliakos Thursday morning after six hours of testimony that ran through the night.

The move comes after the court had ordered three other Golden Dawn lawmakers freed on bail, raising speculation that the state’s case against the men was not strong.

Golden Dawn has 18 seats in the 300-member parliament. The party is known for its Nazi swastika-like flag and Holocaust-denying leadership.

Government spokesman Simos Kedikoglou hailed Thursday’s decision as an important victory for the Greek legal system, calling it “the most dynamic confrontation of a neo-Nazi criminal gang in European, and possibly world, history.”

The crackdown, which included the arrest of more than 10 other party leaders, follows widespread outrage and protests in Greece in the wake of the Sept. 18 killing of an anti-fascist rapper by a suspected Golden Dawn member.

The stabbing death of Pavlos Fyssas, a rapper known as Killah P, reportedly spurred the government to action.

The European Union, Jewish and other international groups have long urged the Greek government to act against Golden Dawn, which has been accused of being behind dozens of vicious attacks on immigrants in Greece.

Golden Dawn leaders have denied the charges against them, saying the arrests were part of a political witch-hunt against the party.