Turkish leaders have promised an investigation into the killing Saturday of prominent pro-Kurdish lawyer and human rights activist Tahir Elci.
Prime Minister Ahmet Davutolgu said it was not clear whether Elci's death was the result of a "terrorist attack" or whether he was caught in crossfire between Kurdish rebels and security forces.
Witnesses to the attack said the assailants opened fire on Elci and other activists while they gave a press statement to a gathering in the mainly Kurdish province of Diyarbakir. The shooting, they said, triggered a firefight between Kurdish rebels and security forces.
Hospital sources said Elci died of a gunshot wound to the head. Two policemen were also killed in the violence.
Elci was chairman of the Diyarbakir Bar Association. Turkish authorities arrested him in October for saying that the outlawed Kurdistan Workers' Party was not a terrorist organization. He was released pending his trial.
"This is a very dark day for Turkey. The murder of Tahir Elci is a devastating blow not only to human rights activists but to all who want to see justice and the rule of law prevail in Turkey," said Emma Sinclair-Webb, a senior researcher at Human Rights Watch.
More than 1,000 people took to the streets of Istanbul later Saturday to protest the killing. Turkish police used tear gas and water cannons to disperse them.