The heaviest violence was seen in Diyarbakir, the main city of the Kurdish-majority southeast, where crowds pelted police with firecrackers but there were also clashes in other Kurdish areas and the largest city, Istanbul.

The Peace and Democracy Party (BDP), Turkey's main Kurdish political movement, urged an extraordinary parliamentary session to resolve the row, warning of fresh unrest in a country long plagued by ethnic conflict.

"It is an issue far beyond the participation of several people in the elections ... It is a process that could drag Turkey into a deep crisis and chaos," BDP leader Selahattin Demirtas said on NTV television.

About 3,000 people gathered in Diyarbakir to protest Monday night's ruling of the Higher Electoral Board (YSK), hurling stones and firecrackers at the security forces who in turn used tear gas and water cannons.

Around 20 people were detained, according to an AFP reporter at the scene.

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

In Istanbul too, police resorted to pepper gas as Kurdish youths hurled Molotov cocktails and stones at cars, buses and buildings, breaking windows and sparking fire inside a post office, AFP reporters said.

Several journalists were injured after coming under a hail of stones in the clashes in the central Aksaray district, where a metro station was also vandalised.

The unrest broke after 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.

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

Petrol bombs sparked small fires at several public buildings and banks, Anatolia said, adding that two policemen were injured when their car hit a barricade set by the demonstrators.

Citing past convictions and legal technicalities, the YSK Monday disqualified 12 candidates from the June 12 elections, among them seven people backed by the 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 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 treshold is already much criticised as a non-democratic means to hinder Kurdish parties, but the ruling Islamist-rooted Justice and Development Party (AKP) has rejected appeals to reduce it.

The vetoed candidates have a right to appeal the ruling.

The BDP has threatened to withdraw all its candidates from the elections if no solution is found to the problem.

The main opposition Republican People's Party Tuesday lent support to convening parliament, currently in recess, for an emergency session to amend electoral rules, while the AKP was still to respond.

"The AKP may attempt to capitalise on this situation. This is a sincerity test for them," Demirtas said.

Analysts say the disqualification of prominent BDP-backed candidates is likely to play into the hands of the AKP, which also enjoys strong popularity among the Kurds.