An unidentified gunman killed a prominent Kurdish lawyer and rights activist on Saturday in what the pro-Kurdish HDP Party called a "planned assassination," urging people to take to the streets in protest.

Witnesses said Tahir Elci was shot in the head after making a statement to media in Diyarbakir, the largest city in Turkey's troubled, mainly Kurdish southeast where he was president of the local bar association. A policeman was also killed in an ensuing exchange of fire.

Elci had been criticized in Turkey for saying the banned Kurdistan Workers Party (PKK) was not a terrorist organization, though he had denounced PKK violence. He was facing trial over his comments which had infuriated state prosecutors.

Elci was involved in representing three VICE News journalists — British citizens Jake Hanrahan and Philip Pendlebury, as well as Iraqi Mohammed Ismael Rasool — after they were arrested by Turkish authorities on August 27 while reporting in Diyarbakir and charged with baseless terrorism offenses. Hanrahan and Pendlebury were released a few days later, but Rasool remains in pretrial detention, held in a maximum-security prison in the southern city of Adana. Elci had remained as lead lawyer on his case.

"We are shocked and saddened by the senseless killing of leading lawyer and human rights defender Tahir Elci in Diyarbakir today," a VICE spokesperson said in a statement. "Tahir was an eminent figure in Turkey's legal system and was involved in representing three VICE News journalists arrested while reporting in the region. One of those journalists, Mohammed Rasool, remains unjustly detained after three months, with the charge of 'assisting a terrorist organization' leveled against him. Our thoughts and condolences go out to his family, friends, and colleagues."

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 Peoples' Democratic Party (HDP) called a protest in Istanbul and condemned Elci's killing, which it described as a "planned assassination" in a written statement.

'The moment the statement ended, the crowd was sprayed with bullets.'

"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.

The HDP said Elci had been targeted by the ruling AKP party and its media and it called for political parties, civil society and professional groups to "raise their voices" in protest.

Turkish President Recep Tayyip Erdogan, who founded the AKP party, said in a speech later that a policeman had also been killed during the attack. "This incident shows how Turkey is right in its determination to fight terrorism," he said.

In Reuters TV footage, Elci can be seen lying on the ground with a head injury, apparently still breathing, with blood streaming onto the ground as people continue to exchange fire.

"The moment the statement ended, the crowd was sprayed with bullets," a local official from the pro-Kurdish HDP party, Omer Tastan, told Reuters.

"A single bullet struck Elci in the head," he said, adding that 11 people had also been injured 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. He did not say if anybody had been detained or not.

The Diyarbakir governor's office declared a curfew in the area after the incident. Bozdag and Ala expressed their condolences. Ala said four investigators will be assigned to the case.

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