Greek riot police clashed with protesters taking part in an anti-fascist rally on Wednesday near the site of the fatal stabbing of a left-wing activist, dpa reported.
Police fired tear gas and used stun grenades to disperse hundreds of protesters who attempted to attack the local police station in the western Athens suburb of Keratsini. Similar rallies were taking place in the northern port city of Thessaloniki and in the southern Mediterranean island of Crete.
Protesters were demonstrating against the killing of musician and anti-fascist campaigner Pavlos Fyssas, 34, by a member of the far-right Golden Dawn party, the most violent act linked to the extremist group to date.
Earlier, unknown assailants attacked the leader of the small right-wing Independent Greek Party, Panos Kammenos when he went to visit the site of the stabbing.
A 45-year-old man, a Golden Dawn supporter has been arrested in connection to the stabbing and was to appear before a prosecutor later in the day.
Pyssas died in a state hospital early Wednesday after being attacked by 15 members of the extreme-right party. He was stabbed outside a cafe in the neighborhood of Keratsini.
At the sight of the stabbing, friends and neighbors could be seen leaving flowers and candles.
Police said he suffered at least two stab wounds to the heart and ribs. One man was arrested after a knife was found in his possession and he admitted to the attack as well as being involved with Golden Dawn.
"Golden Dawn's openly xenophobic, neo-Nazi hatred even goes as far as murdering political opponents. This is shocking and intolerable by any standards, and more so in a European Union country," said Hannes Swoboda, president of the Socialists and Democrats Group in the European Parliament, demanding action after the attack.
"It is crucial that the Greek government and parliament draw clear conclusions and come up with solid proposals on how to stop these violent extremist attacks, including the possibility of banning the party altogether."
Before police announced that the suspect had identified himself as being linked to Golden Dawn, party spokesman spokesman Ilias Kasidiaris described the murder as a "heinous crime" and denied his party's involvement.
Officers said searches were underway in numerous Golden Dawn offices in Athens.
The extreme-right party won 7 per cent of the vote and 18 seats in the 300-seat Greek parliament in elections last year. It has since seen its popularity rise to more than 12 percent according to recent polls.
Golden Dawn supporters, who have expressed admiration for Adolf Hitler, have been accused of carrying out hundreds of racist attacks on members of Greece's large immigrant population.
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