Russia's permanent representative to the United Nations, Vitaly Churkin, has died suddenly in New York on 20 February, a day before his 65th birthday. The cause of death is not known.

In a brief statement, the Russian Foreign Ministry said: "It is with profound regret that we announce that Russia's permanent representative to the United Nations Vitaly Churkin has died suddenly in New York on February 20, a day before his 65th birthday."

Reuters said the Russian Foreign Ministry has declined to give details on the circumstances of his death. However, New York Post quoted sources as saying that the ambassador had died after suffering heart problems.

A US government official however said that Churkin had died of an apparent heart attack, Reuters said. A federal law enforcement official, also speaking on condition of anonymity, said that there appeared to be nothing unusual about the ambassador's death, the news agency added.

It said that Churkin fell ill at the Russian Mission to the UN at around 9.30am local time. He was given CPR and taken to the New York Presbyterian Hospital. He was pronounced dead at 10.55am, the sources said.

Russian news agencies quoted Kremlin as saying that Russian President Vladimir Putin was deeply upset by news of Churkin's death.

Russian Foreign Ministry spokeswoman Maria Zakharova told RT: "He was an outstanding person. He was brilliant, bright, a great diplomat of our age." She said news of Churkin's death was "completely shocking."

His death was also announced during the session of the 71st Ad Hoc Working Group on United Nations General Assembly Revitalisation at the UN headquarters.

Tass news agency quoted Churkin's deputy Pyotr Ilyichev as saying: "The loss sustained by Russia is grave and irreplaceable. Ambassador Churkin remained at this work post until the last minute. He devoted his whole life to defending the interests of Russia and was to be found on the very front lines and in the most stressful posts."

Churkin first hit the international spotlight when he was the foreign ministry spokesman for the then Soviet Union from 1990 until its collapse the following year. The top diplomat, who speaks fluent English, served as deputy Russian foreign minister and ambassador to Belgium and then Canada before taking up his UN post in 2006,

Reuters noted how in 2016, Churkin slammed the then-US representative to the UN, Samantha Power who had earlier accused Syria, Russia and Iran of being responsible for the atrocities there.

"The weirdest speech to me was the one by the US representative who built her statement as if she is Mother Theresa herself. Please, remember which country you represent. Please, remember the track record of your country," Churkin said at the assembly.

Alexey Yaroshevsky RT's Washington DC reporter who interviewed him just two weeks ago said he was shocked over the news.

"Interviewed Churkin just 2 weeks ago. He looked in good health and was very energetic during the interview," Yaroshevsky tweeted.

In a second tweet, he warned against those who were "gloating over Ambassador Churkin's death.

Russia's ambassador to the UK, Alexander Yakovenko expressed his shock and sadness over Churkin's death.

"A top diplomat and a good friend," he tweeted.