ISTANBUL — Two members of a banned leftist group who had held a prosecutor hostage in his office inside a courthouse in Istanbul were killed Tuesday in a shootout with police that left their captive seriously wounded, officials said.

Istanbul’s police chief, Selami Altinok said police had negotiated with the gunmen for six hours before the violent end of the hostage situation.

The prosecutor was shot in the head and several other parts of his body and is in a critical condition, undergoing surgery, Turkish President Recep Tayyip Erdogan said during a visit to Romania.

Nevertheless, he congratulated police for the operation.

Private news agency Dogan earlier Tuesday reported police special forces had entered the building, which was evacuated. It wasn’t clear how the assailants sneaked the arms into the courthouse.

The state-run Anadolu Agency and state television, TRT, identified the prosecutor as Mehmet Selim Kiraz. He is the prosecutor investigating the death of a teenager who was hit by a police gas canister fired during nationwide anti-government protests in 2013.

A website close to the left-wing DHKP-C group said that militants from the banned organization had taken the prosecutor hostage at midday and had given authorities three hours to meet five demands, including forcing policemen held responsible for the teenager’s killing to confess to the death.

The group also demanded that the policemen be tried by “peoples’ courts” and for court officials to drop prosecutions or investigations against people who took part in protests denouncing the boy’s death. The website showed a picture of someone holding a gun to a man’s head with posters from the group in the background.

Deputy Chief Prosecutor Orhan Kapici confirmed that the incident was related to Kiraz’s investigation into the boy’s death.

The DHKP-C, which seeks a socialist state, is considered a terrorist organization by Turkey, the U.S. and the European Union.

The group has carried out sporadic attacks, including a suicide bombing on the U.S. Embassy in 2013 that killed a security guard. The group was more active in the 1970s.