Istanbul (AFP) - An armed leftist group took hostage Tuesday a Turkish prosecutor probing the politically sensitive death of an anti-government protester, threatening to kill him if their demands were not met.

Gunfire was heard at the Istanbul courthouse where the prosecutor, Mehmet Selim Kiraz, was working, the Dogan news agency reported said.

Kiraz was investigating the killing of Berkin Elvan, who died in March last year after spending 269 days in a coma due to injuries inflicted by police in the mass protests of early summer 2013.

In a statement published by Turkish media, the hostage-taking was claimed by the radical Marxist Revolutionary People's Liberation Party–Front (DKKP-C), which has been behind a string of attacks over the last years.

The group published pictures showing one of the militants -- his face concealed by a scarf with the group's red and yellow insignia -- holding a gun to Kiraz's head.

They had also plastered their flags and posters on the walls of his office.

Turkish media said that the group had given a deadline of 3:36 pm (1236 GMT) for the prosecutor to identify the police officers who they say were behind the killing of Elvan or he would be shot.

Their demands also include a "live confession" by the officers responsible.

Elvan succumbed to injuries sustained when he was hit by a tear gas canister fired by police in the mass protests of early summer 2013 against the government of President Recep Tayyip Erdogan who was then premier.

He was aged 15 at the time of his death, which was followed by mass nationwide protests that were also largely put down by the police.

Elvan has since become an icon for the Turkish far-left and his supporters accuse the authorities of covering up the circumstances and perpetrators of his death.