DIYARBAKIR, Turkey (Reuters) - A prominent Kurdish lawyer and rights activist was shot in the head and killed on Saturday, in 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. Videos from the scene showed a gun battle in the street, in which two policemen died, and Prime Minister Ahmet 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 shooting, which took place in the southeastern city of Diyarbakir, showed Turkey was right in “its determination to fight terrorism”.

Elci was facing trial for saying the banned Kurdistan Workers Party (PKK) was not a terrorist organization, as the government describes it. He had, however, denounced PKK violence.

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.

Kurdish forces are fighting Islamic State in both Iraq and Syria, making them an important ally of the United States against the militants -- something Turkey fears could embolden its own Kurdish minority.

Hours after Elci’s death, 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.”

“SPRAYED WITH BULLETS”

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Witnesses said Elci had been shot after speaking to journalists 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.

Despite videos of the shooting from several angles, the sequence of events was unclear.

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. Another video published by local media of the same scene showed two men running past police, who shot at them.

Police surveillance camera footage showed a large yellow cab arriving at the scene and policemen running towards it. Shots were fired from inside the cab as one of them opened the door, and two policemen fell to the ground as the passengers ran away.

Turkish news stations said one of the policemen died at the scene and the other later in the evening.

At a news conference, Interior Minister Efkan Ala said a gun battle erupted after someone shot at police from an unidentified car.

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“Tahir Elci was caught up in fire between police and terrorists,” he said, without saying whether anyone had been arrested.

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.

“STRUGGLE FOR JUSTICE”

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 called for political parties, civil society and professional groups to “raise their voices” in protest.

The Diyarbakir governor’s office declared a curfew in the area after the incident. Interior minister Ala said four investigators would be assigned to the case, and he and the justice minister expressed their condolences.

The U.S. embassy expressed its shock over Elci’s death, calling him on Twitter a “courageous defender of human rights”.

Emma Sinclair-Webb, senior researcher at U.S.-based Human Rights Watch, said: “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 rule of law prevail in Turkey.”

Turkey, the United States and the European Union classify the PKK, which is demanding greater autonomy for Turkey’s Kurds, as a terrorist organization.