Greece's prime minister has vowed to crack down on the neo-Nazi Golden Dawn party.
The murder of an anti-fascist singer by one of the group's supporters has sparked nationwide outrage.
"This government is determined not to allow the descendants of the Nazis to poison our social life, to commit crimes, terrorise and undermine the foundations of the country that gave birth to democracy," Antonis Samaras said in a televised address on Thursday.
The murder early on Wednesday of popular hip-hop artist Pavlos Fyssas, who wrote music under the nickname Killah P, has prompted angry calls for a check on the party's activities.
Thousands of Greeks took to the streets to protest against the killing, a day after police and anti-fascist demonstrators clashed in cities across the country.
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Around 4000 people took to the streets of Athens carrying banners that said "stop fascism" and "no pasaran" ("they shall not pass").
The protesters, mostly trade union members, shouted slogans including "out with fascists" and "workers do not fear threats".
The 34-year-old was fatally stabbed in the working-class Athens district of Keratsini by a 45-year-old truck driver, George Roupakias, who allegedly confessed his Golden Dawn affiliation to police.
The victim's family said that Fyssas and a small group of friends were ambushed by a large gang of Golden Dawn supporters outside a cafeteria.
Golden Dawn quickly denied links with the killer, but pictures soon surfaced of Roupakias participating in party activities, and reports say members of his family worked for the organisation.
