Russian ambassador murder 'provocation' to damage relations: Erdogan

"We know that this is a provocation aimed at destroying the process of normalisation in relations between Turkey and Russia," Erdogan said in televised comments.

Erdogan's remarks come as Turkish police detained the sister and mother of the gunman in southwestern Turkish province of Aydin.

The Russian ambassador was shot by a Turkish policeman at an exhibition in Ankara apparently as an act of revenge for the Russian bombing of Aleppo.

Dramatic footage showed the very moment the gunman - dressed in a dark suit, white shirt and tie, shot at Karlov, who was at the opening of a Russian photography exhibition at an arts centre in Ankara.

The assailant is seen standing behind the ambassador as he is speaking and then swaggering around the exhibition waving his gun and pointing aggressively into the air. 

The man shouted "Allahu Akbar" and spoke in Arabic about pledging allegiance to, the footage shows.

He then switches to Turkish, shouting: "Don't forget about Syria, don't forget about Aleppo. All those who participate in this tyranny will be held accountable."

The state-run Anadolu news agency said the gunman had been "neutralised" in a police operation inside the centre after a 15-minute shootout. 

Moscow and Ankara agreed this summer to normalise ties after a crisis sparked by the shooting down last year by Turkey of a Russian plane over Syria. 

The assassination of Russia's envoy to Turkey will likely not harm warming bilateral ties but its impact may be felt more in Syria.

US Secretary of State John Kerry condemned the attack on Monday, adding that his country was ready to help Russia and Turkey investigate the incident.

US offers helping hand

US Secretary of State John Kerry condemned the attack on Monday, adding that his country was ready to help Russia and Turkey investigate the incident.

"The United States condemns the assassination today in Ankara of Russian Ambassador Andrei Karlov," Kerry said in a statement.

"We stand ready to offer assistance to Russia and Turkey as they investigate this despicable attack, which was also an assault on the right of all diplomats to safely and securely advance and represent their nations around the world."

Agencies contributed to this report.