A Turkish policeman shot dead Russia's ambassador to Turkey in Ankara on Monday, prompting a vow from President Vladimir Putin to step up the fight against "terrorism."
Andrei Karlov died of his wounds after the shooting in an Ankara exhibition centre, which came on the eve of a key meeting in Moscow between the Russian, Turkish and Iranian foreign ministers on the Syria conflict.
Dramatic footage showed the moment the gunman shot the veteran diplomat in the back as he opened a show of Russian photographs.
Images showed the ambassador standing up to speak at a lectern, before stumbling and crashing to the ground as shots ring out, lying flat on his back as the attacker - dressed in a dark suit, white shirt and tie - brandishes his gun at shocked onlookers.
Switching to Turkish, he then says: "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 hall after 15 minutes of clashes when he refused to surrender.
Photos showing the man lying on the ground, riddled with bullet wounds, quickly began to circulate on social media.
Turkish Interior Minister Suleyman Soylu identified the attacker as Mevlut Mert Altintas, 22, who had worked in the Ankara anti-riot police for the last two and a half years.
His mother, father and sister were reportedly detained for questioning in their home in western Turkey.
'Baying for blood'
The killing came after days of protests in Turkey over Russia's role in Syria, although Moscow and Ankara are now working closely together to evacuate citizens from the battered city of Aleppo.
Putin called the killing of Russia's ambassador a "provocation" aimed at sabotaging warming ties between Moscow and Ankara and efforts to resolve the conflict in Syria.
"There can be only one answer to this - stepping up the fight against terrorism, and the bandits will feel this," Putin said at a meeting with Russia's foreign minister and the heads of the overseas and domestic intelligence agencies.
"We have to know who directed the hand of the killer," Putin said.
Turkish President Recep Tayyip Erdogan echoed Putin's comments, saying the killing was aimed at wrecking a normalisation process that had taken root after a crisis sparked when Turkey shot down a Russian plane over Syria.
The UN Security Council would observe a minute's silence on Tuesday to pay tribute to Karlov, said Spanish Ambassador Roman Oyarzun, who holds the body's rotating presidency.
James Nixey, head of the Russia and Eurasia programme at Chatham House think tank in London, said Moscow would use the attack to step up action in what the Kremlin sees as a "war on terror".
"My sense is that the Russians won't blame the Turks for this but will seek to capitalise on it for wider gains," he said.
"Clearly the Russian military will be baying for blood, they'll want revenge."
The shooting took place at the Cagdas Sanatlar Merkezi, a major art exhibition hall in the Cankaya district of Ankara where most foreign embassies are located, including Russia's.
"When the ambassador was delivering a speech, a tall man wearing a suit fired into the air first and then took aim at the ambassador," Hurriyet correspondent Hasim Kilic, who was at the scene, told AFP.
"He ordered the civilians to leave the room. When people were fleeing, he fired again."
Hurriyet said Karlov was the first ambassador to be assassinated in Turkey, although the British consul was killed in an Istanbul bombing in 2003 and Israel's consul general was kidnapped and shot dead by leftist militants in 1971.
Turkey and Russia stand on opposite sides of the Syria conflict with Ankara backing rebels trying to topple Moscow's ally President Bashar al-Assad.
But the tone has warmed considerably since a reconciliation deal was signed earlier this year and a Russian and Turkish-brokered accord has helped the evacuation of citizens from Aleppo in recent days.
The Syrian foreign ministry in Damascus denounced the murder as a "despicable crime", state news agency SANA said.
The foreign and defence ministers of Russia, Turkey and Iran were to meet in Moscow later Tuesday to discuss Syria.
Turkish Foreign Minister Mevlut Cavusoglu learned of the shooting while on the plane to Moscow but insisted the meeting would go ahead as planned.
Born in 1954 in Moscow, Karlov was a career diplomat who had begun his career under the USSR in 1976. He was Russian ambassador to North Korea from 2001-2006.