Turkey's Constitutional Court banned the country's largest Kurdish political party the DTP on Friday, ruling that it supported terrorism, dpa reported.
The ruling means the party is immediately dissolved, with its 37 parliamentarians facing a five-year ban on political activity - including party chief Ahmet Turk.
The decision will come as a major blow to Turkish-Kurdish relations, which had recently thawed after decades of bloodshed and near civil-war in the east of the country.
Turkish politicians have repeatedly claimed the DTP is the political wing of the banned Kurdistan Workers' Party (PKK).
The court ruled that "as an organisation, they have not sufficiently distanced themselves from violence."
"A party with ties to terrorism must be prohibited," the spokesman for the court, Hasim Kilic, said.
Prime Minister Recep Tayyip Erdogan had recently promised a "democratic opening" towards the Kurdish minority, who number around 15 million - or 20 per cent of the population.
The Kurds have long demanded more autonomy, especially greater respect for their own language.
The conflict, mainly between the outlawed PKK and the Turkish army, has left at least 35,000 people dead.