Russian officials say its ambassador to the United Nations has died suddenly in New York City. Vitaly Churkin was 64.

Russia’s UN ambassador Vitaly Churkin dead at 64

A brief statement from Russia’s Foreign Ministry said Churkin died on Monday morning while at work. It provided no information about the circumstances of his sudden death, which came just a day before his 65th birthday.

Sources told the New York Post that Churkin was working at Russia’s Permanent Mission to the UN when he suffered a “cardiac condition” at about 9:30 a.m. ET. He was unconscious and needed CPR while being rushed to New York Presbyterian Hospital, where he later died, the newspaper said.

A moment of silence was observed as Churkin’s death was announced at the United Nations.

Churkin served as Russia’s ambassador to the United Nations since 2006, making him one of Russia’s best-known figures on the international stage. Prior to that, he served as the Ambassador to Belgium and Canada.

We’re working to gather more information.

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Russia’s deputy U.N. ambassador, Vladimir Safronkov, told The Associated Press that Churkin became ill in his office at Russia’s U.N. mission and was taken to Columbia Presbyterian Hospital, where he died Monday. His cause of death wasn’t immediately known.

Churkin has been Russia’s envoy at the United Nations for a little over a decade and was considered Moscow’s great champion at the U.N.

Tremendous loss for Russian diplomacy,” the Russian Embassy in the United States tweeted Monday.

He had a reputation for an acute wit and sharp repartee especially with his American and Western counterparts. He was previously ambassador at large and earlier served as the foreign ministry spokesman.