Russia's ambassador to the UN, Vitaly Churkin, has died at the age of 64, the Russian foreign ministry has confirmed.

Churkin had been Russia's permanent representative to the UN since 2006, having previously held a number of ambassadorial positions.

His death in New York, just a day ahead of his 65th birthday, was unexpected and the cause of death was not immediately known.

Kremlin spokesman Dmitry Peskov said that Russian President Vladimir Putin was deeply upset to learn of Churkin's death.

"The head of state highly valued Churkin's professionalism and diplomatic talent," Peskov said.

The diplomat fell ill in his office at Russia's UN mission and was taken to Columbia Presbyterian Hospital, according to the Associated Press, which quoted Russia's deputy UN ambassador, Vladimir Safronkov.

The long-time ambassador would have turned 65 on Tuesday Credit: AP

UN colleagues have extended their condolences to Moscow.

Britain's UN ambassador, Matthew Rycroft, called Churkin a "diplomatic giant" and a "wonderful character".

Nikki Haley, who became the US ambassador to the UN in January, said Churkin had been a "gracious colleague".

"In my short time at the United Nations, Ambassador Vitaly Churkin showed himself to be a gracious colleague," Ms Haley said in a statement.

"We did not always see things the same way, but he unquestionably advocated his country's positions with great skill. We send out prayers and heartfelt condolences to lift up his family and to the Russian people."

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."