Kurdish crowds clashed with riot police in street demonstrations Tuesday after Turkey's electoral board barred prominent Kurdish candidates from standing in upcoming elections.

About 3,000 people gathered in Diyarbakir, the largest city of the mainly Kurdish southeast, to protest the controversial ruling of the Higher Electoral Board (YSK), pelting the police with stones and fireworks.

The security forces used tear gas and water cannons to disperse the crowd and detained at least five people, an AFP reporter said.

"Our political will cannot be stifled," the protestors shouted, also chanting slogans praising the outlawed Kurdistan Workers' Party (PKK), which has waged a bloody campaign for self-rule in the southeast since 1984.

Similar unrest erupted in the eastern city of Van when the security forces stopped a crowd from marching on the local electoral office, Anatolia news agency reported.

The protestors hurled petrol bombs at the police and on public buildings and banks, sparking small fires, Anatolia said, adding that two policemen were injured when their car hit a barricade set by the demonstrators.

In Istanbul, some 3,000 people staged a sit-in on Taksim Square, disrupting traffic in the heart of the city for more than an hour.

"Blood for blood, revenge!" some protestors shouted as other chanted slogans of loyalty to jailed PKK leader Abdullah Ocalan.

Citing past convictions and legal technicalities, the YSK Monday disqualified 12 candidates from the June 12 elections, among them seven people backed by Turkey's main Kurdish political movement, the Peace and Democracy Party (BDP).

The barred candidates include iconic Kurdish figures, among them Leyla Zana, winner of the European Parliament's human rights award who spent 10 years in jail before being released in 2004.

The BDP threatened to withdraw all its candidates from the elections and urged an extraordinary parliamentary session to discuss a solution to the controversy.

The BDP fielded its candidates as independents in order to circumvent an electoral treshold under which parties are required to garner at least 10 percent of the vote to enter parliament.

The vetoed candidates have a right to appeal the ruling.

Analysts say the disqualification of prominent BDP-backed candidates is likely to play into the hands of the ruling Islamist-rooted Justice and Development Party, which also enjoys strong popularity in the southeast.