Turkish Prime Minister Ahmet Davutoglu has vowed to bring to justice the killers of leading pro-Kurdish lawyer Tahir Elci.
Mr Elci was shot dead in the south-eastern city of Diyarbakir during a battle between police and unidentified gunmen. Two policemen also died.
Mr Elci had been making a speech appealing for peace between security forces and Kurdish separatists when he was shot.
The pro-Kurdish HDP Party called his death a “planned assassination”.
Later, Turkish police used water cannon and tear gas to disperse hundreds of people in Istanbul who were protesting against the killing.