Russia's ambassador to Turkey has been killed in a gun attack in the Turkish capital, the Russian Foreign Ministry has confirmed.

Foreign Ministry spokeswoman Maria Zakharova made the announcement in a live televised statement, saying: "Today in Ankara, as a result of an attack, the ambassador of the Russian Federation to Turkey, Andrey Gennadyevich Karlov, received a wound from which he died.

"We regard this as a terrorist act."

The ambassador had been attending an art exhibition at the Contemporary Arts Centre in the Cankaya area of Ankara, along with other dignitaries and media.

The gunman is understood to have entered the gallery with a police ID and opened fire on the ambassador as he made a speech.

An unnamed gunman gestures after shooting the Russian Ambassador to Turkey, Andrei Karlov, at a photo gallery in Ankara. Picture by Burhan Ozbilici AP/Press Association Images

A video showed him shouting: "Don't forget Aleppo, don't forget Syria!"

According to the private NTV news channel, Turkish police have shot dead the gunman.

Earlier, there were reports of an hostage situation as special forces sealed off the building.

Three other people injured were still inside the gallery, according to reports.

A photographer from Associated Press who had been at the exhibition said the gunman had been wearing a suit and tie and had shouted "Allahu Akbar" before firing at least eight shots.

He had also spoken in Russian and smashed several of the photos in the exhibition.

Hasim Kilic, a correspondent for the daily Hurriyet, told AFP: "He said something about 'Aleppo' and revenge."

In a statement, Foreign Affairs Minister Charlie Flanagan said: “I condemn the brutal assassination of the Russian Ambassador to Turkey.  I offer sincere condolences to Ambassador Karlov’s family and loved ones and to the Government and People of Russia.

"Diplomats play critical role in the conduct of relations between States and today is a bleak day for the diplomatic community around the world.” 

The shooting comes after days of protests in Turkey over Russia's backing of Syrian president Bashar al Assad.

Ankara's mayor Melih Gokcek said the attack was an attempt to ruin Turkish relations with Moscow.

It is unclear who carried out the attack, although Islamic State militants have been active in Turkey and have carried out several bomb attacks on Turkish targets.

Russian Ambassador to Turkey Andrei Karlov at the gallery before the shooting. Picture by Burhan Ozbilici AP/Press Association Images

Russian President Vladimir Putin said his security forces will track down those behind the assassination of the country's ambassador to Turkey.

"The only response we should offer to this murder is stepping up our fight against terror, and the criminals will feel the heat," he said.