Russian Ambassador to the United Nations Vitaly Churkin addresses members of the U.N. Security Council during a meeting about the Ukraine situation, at the U.N. headquarters in New York, March 6, 2015. [FILE PHOTO/Agencies]

Russia's ambassador to the United Nations, Vitaly Churkin, died suddenly in New York on Monday after being taken ill at work, the Russian Foreign Ministry said.

The ministry gave no details on the circumstances of his death but offered condolences to his relatives and said the diplomat had died one day before his 65th birthday.

It declined to comment on reports that Churkin had been taken to hospital shortly before his death.

President Vladimir Putin was "deeply upset" by the news and had greatly valued Churkin's professionalism and diplomatic talent, Russian news agencies quoted the Kremlin as saying.

The New York Post quoted unnamed sources as saying Churkin had been rushed to a Manhattan hospital from the Russian embassy after falling ill with a cardiac condition.

Tass news agency quoted Churkin's deputy Pyotr Ilyichev as saying: "The loss sustained by Russia is grave and irreplaceable.

"Ambassador Churkin remained at his 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."

Foreign ministry spokeswoman Maria Zakharova said on Facebook: "Great diplomat. Extraordinary personality. Colourful man."