It was the third straight day of street violence after the constitutional court outlawed Turkey's main Kurdish party, the Democratic Society Party (DTP), for links with Kurdish rebels who have led a 25-year insurgency in the southeast.

The unrest in central Istanbul, involving some 100 people, erupted following a Kurdish protest over the court ruling.

The demonstration had ended peacefully, but a group of Kurdish youths, some of them masked, embarked on a march, hurling petrol bombs and stones at shops, apartment buildings and cars.

They were confronted by a group of Turkish nationalists and local residents, armed with knives and sticks, and several with guns.

Gunshots were heard as the two groups attacked each other before riot police arrived, firing tear gas to disperse the crowd.

Angry protestors took to the streets also in Diyarbakir, the largest city of the Kurdish-majority southeast, hurling stones and fireworks at the security forces.

The police responded with pepper gas and water cannon. Several people were injured.

Paramilitary soldiers were called in to help the police in the town of Yuksekova, where protestors set barricades in the streets, officials said.

At least 15 people were detained in the two demonstrations.

In Hakkari, the authorities said they captured a demonstrator who had snatched a policeman's gun in street clashes on Saturday.

DTP's closure came atop already simmering tensions after Kurdish rebels killed seven soldiers in an ambush in northern Turkey Monday.

The rebels said the attack was a reprisal for the prison conditions of their jailed leader Abdullah Ocalan, which Kurdish activists claim have deteriorated, and the killing of a Kurdish student in demonstrations last week.

The mounting violence has overshadowed government plans announced in August to expand Kurdish freedoms in a bid to erode popular support for the rebels and end the conflict in the southeast, which has claimed some 45,000 lives.