Fox News reports an off-duty Turkish police officer killed Russia's ambassador to Turkey and wounded at least three others.

The gunman, identified as 22-year-old Mevlut Mert Altintas, was heard on video shouting "allahu akbar" and "don't forget Aleppo, don't forget Syria" as he opened fire at an art gallery in Ankara.

According to the Fox report, Turkish media say the gunman has been killed, and the Turkish Foreign Ministry is calling the killing a terrorist act.

The shooting was caught on video, as Ambassador Andrei Karlov was giving a speech at the Ankara Center for Contemporary Art.

Reports also say Russian President Vladimir Putin is vowing revenge for the attack.