Kurdish demonstrators clashed with police and vandalised shops in Diyarbakir, the main city of the predominantly Kurdish southeast, after about 2,000 people had gathered for the funerals of the four militants.
They were among 14 members of the separatist Kurdistan Workers' Party (PKK) killed over the weekend in a major security operation in the region.
Demonstrators refused to disperse after the ceremony, shouting "vengeance" and hurling petrol bombs, sticks and stones at the security forces, who responded by spraying the crowd with water cannons and tear gas.
At least two armoured police vehicles were briefly set ablaze by petrol bombs. Demonstrators broke the windows of shops and public buildings and stoned ambulances sent to the scene to pick up injured people.
Several dozen paramilitary officers were called in to reinforce the police presence and at least one of them was seen firing warning shots in the air.
Two policemen were stabbed, and one was in serious condition, medical sources said. Three journalists were also among the injured. The governor's office said 23 protesters were detained.
Similar unrest took place in the southern city of Adana during the funeral of a fifth PKK rebel, the NTV news channel reported.
Tension in Turkey's southeast has markedly escalated since June 2004 when the PKK called off a unilateral ceasefire.
The PKK has been blacklisted as a terrorist group by Ankara, the European Union and the United States.
The conflict has claimed some 37,000 lives since 1984 when the
PKK took up arms for Kurdish autonomy in the region.