A prominent Kurdish lawyer and rights activist has been shot in the head and killed in a street shootout, an incident likely to fuel further unrest in Turkey's mostly Kurdish southeast.
The pro-Kurdish HDP Party called the killing of Tahir Elci a "planned assassination" and urged people to protest.
Prime Minister Ahmet Davutoglu said it was unclear whether Elci was caught in crossfire or assassinated.
Hours later, police fired tear gas and water cannon to disperse hundreds of people marching in Istanbul to protest against the killing. The marchers chanted: "Shoulder to shoulder against fascism," and "Tahir Elci is immortal."
Reuters TV footage showed plain clothes police repeatedly shooting at a figure running past them towards Elci. He was then seen lying on the ground with blood apparently streaming from his head.
Witnesses said Elci was shot by a single bullet after speaking to media in the southeastern city of Diyarbakir, where he was president of the local bar association. Two policemen also died in gun battles.
It was difficult to piece together the sequence of events from videos showing the incident from different angles.
Privately owned Dogan News Agency reported two police officers were wounded when an investigative team, including Diyarbakir's chief prosecutor, visited the site and came under fire.
Elci had been criticised in Turkey for saying the banned Kurdistan Workers Party (PKK) was not a terrorist organisation, as the government describes it. He had, however, denounced PKK violence.
He was facing trial over his comments, which had infuriated state prosecutors.
Hundreds of people have been killed since a ceasefire between the PKK and Turkish security forces collapsed in July, reigniting a conflict in which some 40,000 people have died since it began in 1984.
The pro-Kurdish HDP, whose initials stand for Peoples' Democratic Party, called a demonstration in Istanbul.
"In the place left by Tahir Elci, thousands more Tahir Elcis will carry on the work in the struggle for law and justice," it said in a statement.
The HDP said Elci had been targeted by the ruling AK party and its media and it called for political parties, civil society and professional groups to "raise their voices" in protest.
Prime Minister Davutoglu said it was unclear whether Elci was caught in crossfire or assassinated. If it was the latter, he said, the target was clear. "The target is Turkey. It's an attack on peace and harmony in Turkey."
President Tayyip Erdogan said the incident showed Turkey was right in "its determination to fight terrorism".
'SPRAYED WITH BULLETS'
Witnesses said Elci had been shot after speaking about a historic minaret which had been damaged in clashes days before.
"The moment the statement ended, the crowd was sprayed with bullets," a local HDP party official, Omer Tastan, told Reuters.
"A single bullet struck Elci in the head," he said, adding that 11 people had also been wounded in the incident.
At a news conference with Justice Minister Bekir Bozdag, Interior Minister Efkan Ala said a gun battle erupted after someone shot at police from an unidentified car.
"Tahir Elci was caught up in fire between police and terrorists," he said, without saying whether anyone had been arrested.
Police surveillance camera footage shows a large yellow cab arriving at the scene and policemen running towards it. They are fired at from inside the cab as one of them opens the door, and two policemen fall to the ground as the cab passengers run away.
Turkish news stations said one of the policemen died at the scene and the other later in the evening.
The Diyarbakir governor's office declared a curfew in the area after the incident. Bozdag and Ala expressed their condolences. Ala said four investigators would be assigned to the case.
The U.S. embassy expressed its shock over Elci's death, calling him on Twitter a "courageous defender of human rights".
Turkey, the United States and the European Union classify the PKK, which is demanding greater autonomy for Turkey's Kurds, as a terrorist organisation.
