Russian Ambassador to Turkey Assassinated in AnkaraA gunman believed to have been an off-duty policeman shot and killed Russia's ambassador to Turkey Monday night in Ankara. Ambassador Andrey Karlov was making a speech at the opening of an art gallery exhibition when a man dressed in a suit approached the podium and opened fire. The entire scene was captured on video. The assassin yelled "Allahu Akbar" and vowed to avenge what he says are Russian murders of innocent people in Syria, pointing his pistol at the ceiling and briefly at the the audience while the mortally wounded ambassador lie on the floor.  One witness told VOA the gunman shouted "Do not forget Aleppo! Do not forget Syria! As long as our lands aren't safe, you will not be safe." Three other people were also wounded before security officers shot the gunman dead. Ambassador Karlov died at a hospital. Ankara Mayor Melih Gokcek has identified the assassin as a 22 year-old police officer who may have been off duty. Russian President Vladimir Putin condemned the killing as an act of terrorism. "There is no doubt that the committed clime is a provocation aimed at ruining Russian-Turkish relations and the peace process in Syria which is moving forward with the help of Russia, Turkey, and Iran," Putin said. "The answer is to strengthen the counter-terrorism efforts and the criminals will feel that soon."  White House spokesman Ned Price said the U.S. strongly condemns the assassination and sends its condolences to the victims. "This heinous attack on a member of the diplomatic corps is unacceptable and we stand united with Russia and Turkey in our determination to confront terrorism in all of its forms." German Interior Minister Thomas De Maiziere said "irrespective of the differences we have with Turkey on other issues, we are in solidarity with Turkey in the common fight against terrorism."  Karlov has been Russia's ambassador to Turkey since 2013. Ties between Russia Turkey have been slowly improving since Turkish jets shot down a Russian bomber that strayed into its airspace from Syria last year. Russian and Turkish officials have been working together to resolve the refugee crisis in Aleppo, caused, in part, by Russian airstrikes on Syrian rebels. WATCH: Emergency vehicles respond to scene of shooting No media source currently available