The gunman who assassinated Russia's ambassador to Ankara, Andrey Karlov, at an art exhibition Monday shouted out "Aleppo" and "revenge" as he fired, according to an eyewitness account.

"While the ambassador was delivering a speech, a tall man wearing a suit fired into the air first and then took aim at the ambassador," Hasim Kilic, a correspondent for the Turkish daily Hurriyet, told AFP. "He said something about 'Aleppo' and 'revenge'."

Other eyewitnesses said he called out to the ambassador before shooting that he and his country will pay for their anti-Syrian actions in Aleppo.

The attack came after days of protests in Turkey over Russia's role in Syria.

According to information released by Turkish authorities the gunman was a 22-year-old Turkish police officer connected to the Syrian rebels and named Marat Altintas. who entered the room under the guise of a journalist. Security forces tracked down the suspect and after a short exchange of gunfire he was shot dead.

Three others present were injured by the killer and were taken to hospitals.

Russia issued an official announcement of the ambassador's death, emphasizing that the event is seen as "a terrorist act with all its implications."

The US State Department publicized a condemnation of the attack on the Russian ambassador to Turkey, saying: "We condemn this violent act. Our thoughts and prayers are with the family of Ambassador Karlov".