A gunman shouting "Do not forget Aleppo!" assassinated Russia's ambassador to Turkey at an Ankara art gallery on Monday, a report said.

The gunman, described by Turkish officials as a 22-year-old off-duty police officer, also wounded at least three others in the assault on the envoy, Andrey G Karlov, reported the New York Times.

Turkish officials said the assailant was killed by other officers in a shootout.

In televised remarks, Russian President Vladimir Putin said the killing was a clear "provocation" aimed at undermining not just the normalization of Russia-Turkish relations but the "peace process in Syria" promoted by Russia, Turkey, Iran and other countries.

"The only response we should offer to this murder is stepping up our fight against terror, and the criminals will feel the heat," he said.

Turkish President Recep Tayyip Erdogan said the assassination was intended to destroy the normalization of Turkey-Russian relations."But the Russian government and the Turkish republic have the will to not fall into that provocation,” he added.