Mehmet Selim Kiraz was critically injured and two of his captors killed after security forces stormed the building where a far-left group had taken the prosecutor hostage.

Police chief Selami Altınok said officers stormed the building after hearing gunshots and killed two of the gunmen.

The emergency began at 2.36pm local time  when members of the Revolutionary People's Liberation Party-Front stormed into the office of Mr Kiraz.

Images of a masked militant holding a gun to Mr Kiraz's head were then posted on the group's Facebook page, along with a demand for police to confess on live TV within the hour.

Revolutionary People's Liberation Party-Front demanded police confess to killing 15-year-old Berkin Elvan today.

The prosecutor was leading an investigation into the death of 15-year-old Berkin Elvan who was severely wounded after being hit on the head by a tear-gas canister fired by a police officer during anti-government protests in Istanbul in June 2013.

After spending 269 days in a coma, Elvan eventually died on March 11 last year. His death, and the subsequent investigation, have since become a rallying point for the country's far-Left.