The assassin was identified as a Turkish special forces police officer, Ankara Mayor Melih Gokcek told AFP.
Three other people were reportedly hurt.
The camera pulls back to show a smartly dressed gunman, wearing a suit and tie, waving a pistol and shouting.
The Kremlin said President Vladimir Putin had been informed.
Erdogan called Putin after the assassination to share information, according to Turkey's NTV television, which cited the Turkish president's spokesman. "We regard this as a terrorist act".
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"The Syrian republic condemns in the strongest terms the cowardly terrorist attack that led to the death of the Russian ambassador in Turkey, Andrei Karlov", a ministry statement said.
The Russian ambassador to Ankara was shot dead in a brazen attack by a Turkish policeman in a cultural centre on Monday in what both sides branded an "act of terror". "Everyone who has taken part in this oppression will one by one pay for it". He had also been a central conduit to the Turkish government's rapproachment with Moscow in April. The attacker then targeted Karlov, he confirmed.
Since September 2015, Russian Federation has backed the government of Bashar al-Assad in Syria in its war against opposition forces, Turkey continues to support Syrian rebel groups the Kremlin repeatedly refers to as terrorists.
Russian Federation has been a very close ally to Syria in the countless bombing and recapturing of the rebel held city of Aleppo where countless civilians where killed by airstrikes and "shot dead on the spot" by pro-Regime forces.
"We condemn this act of violence, whatever its source", said USA state department spokesman John Kirby.
Indeed, the shooting comes just one day before Turkey's foreign minister was scheduled to fly to Moscow for a meeting with Russian and Iranian diplomats on the situation in Syria.
Russian Federation and Turkey have both been involved in the conflict in Syria, which borders Turkey.