The president of the bar association in southeastern Diyarbakir province has been shot dead by unidentified gunmen while giving a public speech.

A campaigner for Kurdish rights, Tahir Elci had been criticized for challenging Turkey's official stance of calling the Kurdistan Workers Party (PKK) a terrorist organization.

Elci died of gunshots to the head, hospital sources confirmed.

After making comments about PKK on CNN Turk TV in October, Elci was detained. He was subsequently released and had been awaiting trial.

The killing took place while Tahir Elci was making a statement to the media. According to the state Anadolu news agency, it was Kurdish insurgents that opened fire, killing Elci, as well as a police officer, and injuring three other people, among them correspondents of the leading Turkish media organizations – the Anatolia and Dogan news agencies.

Two policemen were also killed in the attack, officials said, adding that one officer had been shot dead on the spot while another died of his injuries later in hospital.

A gun battle erupted after gunfire was opened at police from an unidentified car, Interior Minister Efkan Ala told the media. The official did not mention if anyone had been detained, Reuters reported.

The attack in which Elci was killed might be "an assassination," Prime Minister Ahmet Davutoglu said on Saturday in a televised speech, Hurriyet Daily News reported. But "there are two possibilities," the PM added, saying that the other might be an accident, with the lawyer having been caught in an exchange of fire between security forces and attackers.

A curfew was declared in the region.

#Turkish President #Erdogan just claimed Tahir #Elci's killing was work of #PKK, despite fact that Elci was pro-#Kurd activst & defended PKK — William Whiteman (@willmwhiteman) November 28, 2015

Pro-Kurdish Peoples' Democratic Party (HDP) described Elci's killing as a "planned assassination," Reuters reported citing HDP's statement, which added: "In the place left by Tahir Elci, thousands more Tahir Elcis will carry on the work in the struggle for law and justice."

Tahir Elci studied law in Europe and took part in many high profile cases in the Turkish courts. The lawyer was among the founding members of many human rights and non-governmental organizations.

“The moment the statement ended, the crowd was sprayed with bullets,” Reuters cited Omer Tastan, a local official from the pro-Kurdish HDP party, as saying.

“A single bullet struck Elci in the head,” Tastan said, adding that 11 people were also wounded in the incident.

Dogan News Agency recorded a video of the incident, showing a group of gunmen hiding behind the minaret of a nearby mosque close to where Elci was making his statement. When he finished speaking, the group opened fire at the lawyer and people standing beside him.

“A person ran towards Tahir Elci, fired and then started to run away,” Dogan news agency’s reporter Felat Bozarslan recalls.

#Protest due to take place at 5pm local time today in #Istanbul over killing of Tahir #Elci in #Diyarbakır — William Whiteman (@willmwhiteman) November 28, 2015

The PKK demands greater autonomy for Turkey's Kurds and is classified as a terrorist organization in Turkey and the US.

After the ceasefire agreement between the PKK and Turkish security forces ended in July, hundreds of people were killed in terror acts and clashes in addition to the estimated 40,000 who have died since the Kurds started their armed struggle for autonomy in 1984.