The unanimous verdict from the 11 judges of the Constitutional Court against the Democratic Society Party (DTP) sent hundreds of demonstrators chanting "revenge" onto the streets of Diyarbakir, the largest city in the mainly Kurdish southeast.

At the end of four days of deliberations, the court decided 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 a news conference here.

He said DTP chairman Ahmet Turk and fellow lawmaker Aysel Tugluk had been stripped of their parliamentary seats as well as being banned from politics for five years along with 35 other party members.

All party assets would be seized by the Treasury, Kilic added.

In his first reaction to the verdict, Turk said the ban would not help efforts to secure an end to a 25-year bloody campaign by Kurdish rebels for self-rule.

"Turkey cannot resolve this problem by closing down parties," Turk told reporters here, warning of possible unrest among the Kurdish community.

He hinted that his party stood behind the decision for its 21 lawmakers in the 550-seat parliament to resign from their seats - a move that could raise the possibility of a by-election.

The DTP is scheuled to meet on Saturday to review the verdict and hold a press conference.

Turkey's chief prosecutor started the case against the DTP in 2007, arguing that the party had links with the outlawed Kurdistan Workers' Party (PKK), which has been fighting since 1984 for Kurdish self-rule in a conflict that has claimed about 45,000 lives.

The DTP says it has "no organic links" with the PKK but insists the rebels should be part of efforts to resolve the Kurdish conflict, a suggestion Ankara categorically rejects.

It also refuses to brand the PKK a terrorist group like Turkey and much of the international community. Party members often express support for the rebels and their jailed leader Abdullah Ocalan.

Shortly after the verdict was announced, some 1,000 people gathered outside the DTP offices in Diyarbakir, chanting "Blood for blood! Revenge!".

Some protestors hurled petrol bombs at the police, targeted them with slings, and smashed the security cameras of nearby banks. Riot police responded with tear gas and water cannons.

A crowd of about 100 protestors also gathered at the DTP office in Istanbul, Turkey's largest city with a sizeable Kurdish migrant community, brandishing a banner that read "An End to the Attacks on the Kurdish People".

"We are all Kurds, we all belong to the DTP," chanted the crowd.

Political analyst Ahmet Insel warned that Friday's verdict "amounts to totally torpedoing" the government's plan, launched in August, to expand Kurdish rights in the hope of ending PKK violence.

The plan, which the government insists it will not abandon, has already created a nationalist backlash for granting specific group rights for Kurds and deemed inadequate by Kurdish activists.

The closure of the DTP could also trigger an escalation of violent street protests in Turkish cities, Wolfango Piccoli from the Eurasia group, a London-based political risk consultancy firm, said.

Kurdish protests flared in the southeast at the weekend, with one person shot dead, following claims that Ocalan's prison condition had deteriorated.

"In the aftermath of the court's ruling and with ethnic tensions running very high, there is a risk that...violent protests could turn into clashes between groups of Turkish and Kurdish nationalists," he said in a research note.

The verdict could also create possible further complications for Turkey's troubled bid to join the European Union which has put pressure on Ankara to improve minority rights, he added.

The DTP, which became the 27th party to be banned in Turkey, was founded in 2005 as a successor to several Kurdish parties that were also outlawed for collaborating with the PKK.