Turkish President Recep Tayyip Erdogan spoke by phone with Russian President Vladimir Putin to share information about the shooting of Moscow's ambassador to Ankara, a Turkish official said.
The Russian foreign ministry confirmed the death of envoy Andrei Karlov.
"We regard this as a terrorist act," said Russian Foreign Ministry spokeswoman Maria Zakharova. "Terrorism will not win and we will fight against it decisively."
The attacker was smartly dressed in black suit and tie, and standing behind the ambassador as he made his speech at an exhibition, a person at the scene told Reuters.
"He took out his gun and shot the ambassador from behind. We saw him lying on the floor and then we ran out," said the witness, who asked not to be identified.
Two security sources identified the gunman as an off-duty police officer who worked in the Turkish capital.
A video showed the attacker shouting: "Don't forget Aleppo, don't forget Syria!" As screams rang out, he could be seen pacing about and shouting as he held the gun in one hand and waved the other in the air.
Another photograph showed four people including what appeared to be the ambassador lying on the floor.
The US State Department condemned the attack.
The United Nations condemned an attack on the Russian ambassador to Ankara, who was shot and killed in an attack at an art gallery in the Turkish capital today.
"We condemn the gun attack on the Russian ambassador to Turkey. There can be no justification for an attack on a diplomat or an ambassador," UN spokesman Stephane Dujarric said. "We hope that the perpetrator will be brought to justice."
Image of gunman lying dead after police "neutralised" him.
— Çağla Pınar Kurtman (@caglakurtman) December 19, 2016
Gunman said to be 22-year-old Turkish police officer Mert Altintas.
— Diego Cupolo (@DiegoCupolo) December 19, 2016
The ambassador had been part of discussions between Turkey that led to an evacuation of east Aleppo getting underway late last week.
The incident comes a day before the Turkish foreign minister, Mevlut Cavusoglu, is due in Moscow for talks with Russian and Iranian counterparts.
Fatih Oke, the press attache of Turkey's embassy in Washington DC, wrote on Twitter: "The bullet to Ambassador Karlov is not only aims him. It aims also Turkish Russian relation. We are praying for his good health and peace."
The bullet to Ambassador Karlov is not only aims him. It aims also Turkish Russian relation. We are praying for his good health and peace. pic.twitter.com/jiAkJMHOSC
— Fatih Öke (@okefatih) December 19, 2016
Security around the Russian embassy in Ankara has been stepped up after the Russian ambassador was shot by a gunman, the RIA news agency reported this evening.
— Aldin Abazović (@Ald_Aba) December 19, 2016
Moment of the attack
— Mikhail D. (@Eire_QC) December 19, 2016
Reuters reports Russian Ambassador to Turkey Andrei Karlov has died after he was shot at an art gallery in Ankara.
Police "neutralised" the gunman following the attack.
Images of assailant circulate on social media:
— Aldin Abazović (@Ald_Aba) December 19, 2016
The Russian ambassador to Ankara was seriously wounded in a gun attack in the Turkish capital today and was taken to Guven hospital in Cankaya immediately, NTV and other broadcasters reported.
Russian Ambassador to Turkey Andrei Karlov as been shot multiple times at an exhibition in Ankara, Turkey. Karlov was delivering a speech at the opening ceremony of a photo exhibit "Russia in the eyes of Turks" at the Modern Art Centre when an armed assailant opened fire on him. The envoy was seriously wounded and was taken to hospital immediately, the Anadolu Agency has reported.
Turkish television alleged the gunman shouted: "We'll make you pay for Aleppo." Other reports said the assailant shouted: "We die in Aleppo, you die here. "
The assailant was "neutralised" during an operation by special forces at the scene, Anadolu added.
Russian Foreign Ministry spokeswoman Maria Zakharova confirmed to Russian news agencies that the Russian Karlov had been gunned down in an attack and hospitalised.
Zakharova said Moscow was in touch with Turkish authorities about the attack.
"Today, during a public event, an unknown person opened fire chaotically," Zakharova was cited as saying. "As a result, Andrey Karlov, the ambassador to Turkey, received a gunshot wound."
Kremlin spokesman Dmitry Peskov told the Interfax news agency that President Vladimir Putin had been told about the attack and would be studying a report from the intelligence services and foreign ministry on the incident.
CNNTurk tweeted a picture of the incident:
— CNN Türk (@cnnturk) December 19, 2016
Acc to Hurriyet rep D.Zeyrek, Russian Amb is still in art gallery w gunman. Turkish police forces getting ready for an operation. #ankara
— ilhan tanir (@WashingtonPoint) December 19, 2016
No further details are available at this time.