Two thousand people joined a rally in Athens organised by Golden Dawn to mark the anniversary of the 1996 Imia crisis that brought Greece and Turkey to the brink of war.
Party members held torches and waved Greek and party flags as they marched from the Golden Dawn's main office in northern Athens to the nearby Ministry of Defence.
In central Athens, meanwhile, anti-fascist counter-demonstrators gathered in defiance of a government ban on gatherings in the centre of the city.
Police put the number of people at the Golden Dawn rally at 2,000 with around 500 counter demonstrators in central Athens.
In January 1996, Greece and Turkey clashed over the sovereignty of a handful of rocky islets, called Kardak by Ankara and Imia by Athens, situated a few miles from the Turkish mainland.
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The two countries sent marines to two neighbouring islets in a sign of an imminent armed confrontation, but then withdrew their troops after heavy diplomatic pressure by the United States.
Greek authorities on Friday announced a ban on all public gatherings in central Athens to avert any clashes between nationalist activists and anti-fascists counter-demonstrators.
Police concerns were also raised after 12 Germans, thought to be members of a nationalist group who arrived in Athens to take part in Saturday’s event, were attacked on Thursday by anti-fascists.