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 banned 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 as he went to buy bread during mass demonstrations that began in Istanbul and spread across Turkey.
After nine months in a coma he eventually died in an Istanbul hospital.
Recep Tayyip Erdogan, now Turkey’s president, inflamed passions shortly after the teenager’s death when he said the boy had been carrying a slingshot and had been “taken up into terrorist organisations”.
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.
A website close to the group has published a series of demands, including calls for an immediate confession from police officers responsible for the boy’s death, and for an end to prosecutions of protesters charged over the clashes.
Turkish special forces have entered the court 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 told BBC Turkish.
The DHKP-C is considered a terrorist group by Turkey, the European Union and US. It said it carried out a suicide bombing in February 2013 at the US embassy in Ankara, where a security guard was killed.
In January, a man linked to the banned Marxist group was arrested near the prime minister’s offices in Istanbul, reportedly after throwing two grenades that failed to explode.
(Source: BBC)
