A prominent lawyer and human rights defender, who faced a criminal charge for supporting Kurdish rebels, has been killed in an attack in south-east Turkey.

Tahir Elci was shot while he and other lawyers were making a press statement. A police officer also died in the attack, and two policemen and a journalist were injured.

It was not immediately clear who was behind the attack and there were conflicting reports about what led to it.

Interior minister Efkan Ala and other officials said the assault was against police officers, and that Mr Elci died in an ensuing clash. But the Diyarbakir Bar Association said the lawyer, who was Kurdish, was the target of the attack.

Mr Elci, 49, was the head of the bar association in the mainly Kurdish city and a human rights activist.

He was briefly detained and questioned last month for saying during a live news programme that the Kurdistan Workers' Party, or PKK, is not a terrorist organisation.

Soon after, he was charged with making terrorist propaganda and was facing more than seven years in prison.

Turkey and its allies consider the PKK to be a terrorist organisation, and the government has stepped up attacks against it in recent months.

The PKK has been fighting for autonomy in south-eastern Turkey since 1984.

Mr Ala said the attack began with two people firing at police from an area some 100 yards away from where Mr Elci was speaking. A policeman died in that attack. Mr Ala said Mr Elci died soon after in a clash between the police and assailants.

Prime Minister Ahmet Davutoglu spoke of two possible scenarios.

"One possibility is that after this terror attack, the assailants assassinated Mr Elci," Mr Davutoglu said. "A second possibility is that ... Mr Elci got caught in the crossfire."

Mr Davutoglu vowed to find the culprits through a "transparent" investigation and promised no cover-up.

A government official said four inspectors have been assigned to investigate the case, adding that the government was "determined to shed light" on the attack.

He said authorities believe that Mr Elci was caught in the crossfire, but were not ruling out "the possibility that a third party directly targeted him".

Mr Elci had said through his Twitter account that he had received death threats because of his televised comments in which he defended the rebels.

Authorities declared a curfew in the Sur neighbourhood where the attack occurred - a scene of frequent clashes between security forces and Kurdish youths.

Protests later broke out in Diyarbakir and elsewhere denouncing the killing.

In Diyarbakir, police used pressurised water against a group of protesters who hurled rocks and fire crackers. Police also dispersed hundreds of people who had gathered in central Istanbul chanting: "We are all Tahir, we are all Elci."

At the time of the attack, Mr Elci and other lawyers were making a statement about the destruction caused to a historic mosque by the clashes in Sur. Mr Elci had strongly advocated an end to the renewed violence between the PKK and security forces.