Photo: Twitter.com as posted on the profile of aysekosan123@gmail.c

A prosecutor in Turkey has been taken hostage by an armed anti-government group, according to Turkish media reports.

A photograph of an armed man holding a gun to the head of prosecutor Mehmet Selim Kiraz at a courthouse in Istanbul has been displayed on social media.

Mehmet Selim Kiraz had been investigating the controversial death of Berkin Elvan, who had died a year ago after 269 days in coma caused by police violence during the mass anti-government protests of summer 2013.

The Revolutionary People's Liberation Party-Front (DHKP/C) claimed responsibility for taking the prosecutor hostage through social media. In a statement posted online the banned Marxist group threatened to kill Kiraz if the officer who shot Berkin was not arrested immediately.

The deadline for the ultimatum was set for 15:35 local time. Special Turkish government forces have launched an operation to free the prosecutor.