Tensions began on Sunday morning when Kurdish demonstrators in Istanbul threw stones and firebombs during a rally to protest the solitary confinement of imprisoned Kurdish rebel leader Abdullah Ocalan.
Later, paramilitary police blocked thousands of other pro-Kurdish demonstrators from reaching the northwestern port town of Gemlik to stage an unauthorised demonstration. The port is used by Ocalan's lawyers to travel to the prison island of Imrali, where the rebel leader is the only inmate.
Paramilitary troops stopped dozens of buses packed with demonstrators before they could reach Gemlik, in the western province of Bursa.
On their return, angry Turkish nationalists stopped the convoy at a makeshift roadblock in downtown Bozuyuk, in Bilecik province, set car tires on fire and smashed the windows of the buses with stones, video footage showed.
Several demonstrators were reported to be injured. Nationalist Turks are fiercely against any concessions towards Kurdish rebels who have been fighting for autonomy in southeast Turkey in a conflict that has claimed the lives of 37,000 people since 1984.
The protesters were confronted
by nationalist Turks
The semiofficial Anatolia news agency said some demonstrators were injured when the windows of the buses were smashed. Some Kurdish demonstrators clashed with the nationalists and some police officers were also reportedly injured by flying stones, local reporters said.
Police evacuated at least five injured demonstrators, including a man with a bloodied face, from the scene in an armored personnel carrier, the footage showed.
Paramilitary troops and police were reinforced in the town and the situation was still tense.
Earlier in Istanbul, riot police used tear gas and pepper spray to break up hundreds of Kurds who attacked police with stones and firebombs. Police detained 88 demonstrators.
Ocalan's Kurdish rebel group, the Kurdistan Workers Party, or PKK, announced a unilateral cease-fire on 19 August after Prime Minister Recep Tayyip Erdogan vowed to improve economic conditions in predominantly Kurdish areas and offer greater cultural freedoms for Kurds.
Protesters reject the solitary
confinement of Ocalan
The United States and European Union list the PKK as a terrorist organisation. Turkish officials have not responded to the truce, and military officials have repeatedly said that they will fight until all rebels surrender or are killed.
A senior rebel commander, Murat Karayilan, accused Turkey of not responding in kind and said he would not be "held responsible" if violence increased after the one-month cease-fire expired on 20 September, the pro-Kurdish Ozgur Gundem newspaper reported.
In fresh violence on Sunday, Turkish troops killed two Kurdish rebels near the southeastern city of Tunceli, the Anatolia news agency reported.