— El Puntano (@ElPuntanoCom) December 19, 2016

Photos show the attacker moments before the assassination:

https://twitter.com/OldBlackHack/status/810892043635589120

The UK Mirror reported:

Russia’s ambassador to Turkey has been assassinated in front of terrified witnesses allegedly in retaliation for the crisis in Aleppo.

The gunman reportedly said in Turkish “We die in Aleppo, you die here” during the shooting which left Ambassador Andrei Karlov dead.

The attacker was fatally shot by police after wounding Mr Karlov and at least three others, according to state TV.

Mr Karlov was delivering a speech at an art gallery in the capital of Ankara when the gunman fired a shot into the air and then shot the ambassador in a suspected radical Islamic attack, the Hurriyet newspaper reported.

UPDATE:

The assailant has been identified as Mert Altintas and was reportedly an on-duty police officer.