Turkey's Constitutional Court has voted to ban the country's largest pro-Kurdish party because of alleged links with Kurdish separatist rebels.
Turkey's chief prosecutor Abdurrahman Yalcinkaya argued that the Democratic Society Party (DTP) took orders from the Kurdistan Workers Party (PKK).
The DTP is the latest in a series of pro-Kurdish parties to have been closed down in Turkey.
The EU, which Turkey hopes to join, expressed concern over Friday's ruling.
"While strongly denouncing violence and terrorism, the presidency recalls that the dissolution of political parties is an exceptional measure that should be used with utmost restraint," the EU's Swedish presidency said in a statement reported by Reuters.
The 11 judges in Turkey's Constitutional Court ruled that the DTP had become a "focal point of activities against the indivisible unity of the state, the country and the nation", court president Hasim Kilic told reporters.
He said DTP leaders Ahmet Turk and Aysel Tugluk had been stripped of parliamentary immunity and banned from politics for five years along with 35 other party members.
All party assets would be seized by the treasury, Mr Kilic added.
The DTP holds 21 seats in Turkey's 550-member parliament.
Some 40,000 people have died since the outlawed PKK launched an armed campaign in the mainly Kurdish south-east in 1984.
The BBC's Jonathan Head, in Istanbul, says the DTP's ban is another blow to the government's hopes of ending the conflict.
Prime Minister Recep Tayyip Erdogan has tried to push through a package of reforms aimed at winning over the alienated Kurdish community and persuading militants to lay down their weapons.
Reacting to the ban, DTP chairman Mr Turk said it would not help to end the 25-year conflict.
"Turkey cannot resolve this problem by closing down parties," he said.
The court case has already caused unrest in Kurdish areas.
In the city of Hakkari - near the Iran and Iraq borders - Turkish police used water canon to break up a protest by Kurdish rebel supporters on Friday, Anatolia news agency reported.
Kurds make up about 20% of Turkey's population of more than 70 million.
The PKK is listed as a terrorist organisation by Turkey, the EU and the US.