Armed men have taken hostage the Turkish prosecutor heading the inquiry into the death of a boy during anti-government protests in 2013.
Dramatic images have emerged on social media of a gun being held to the head of Mehmet Selim Kiraz at a court house in Istanbul.
A Marxist revolutionary group is suspected of being behind the incident.
A statement posted online said the prosecutor would be killed if their demands were not met.
Berkin Elvan, who was then 14, was struck in the head by a police tear gas canister in June 2013 during mass demonstrations that began in Istanbul and spread across Turkey.
After nine months in a coma he eventually died in an Istanbul hospital.
Suspected members of the Revolutionary People’s Liberation Party-Front (DHKP-C) took the prosecutor hostage on the sixth floor of the Caglayan court house, reports said.
Demands then circulated in Turkish media, including an immediate confession from police officers responsible for the boy’s death and an end to prosecutions of protesters charged in relation to the clashes.
Turkish special forces have entered the building, which has been evacuated.
Berkin Elvan’s father appealed for the prosecutor to be freed: “My son is dead but let no-one else die.”
“You can’t wash blood with blood,” he said in words quoted by Turkish MP Huseyin Aygun.