NEW YORK >> Russia’s ambassador to the United Nations, Vitaly Churkin, died suddenly after falling ill today in his office at the mission, Russian officials said.

Churkin, 64, was rushed to a hospital in New York, where he died, Russia’s deputy U.N. ambassador, Vladimir Safronkov, told the Associated Press. His cause of death wasn’t immediately known.

Churkin had been Russia’s envoy at the United Nations since 2006 and was considered Moscow’s great champion at the U.N. He had a reputation for an acute wit and sharp repartee, especially with his American and Western counterparts. He was currently the longest-serving member of the Security Council, the U.N.’s most powerful body.

Among many other issues, he had recently made Russia’s views heard on the conflict in close ally Syria, sparring with diplomats from the U.S. and other Western countries over whether to impose sanctions or take action to end the conflict in Syria.

President Vladimir Putin had been notified of the death, according to the state news agency TASS.

“The president was grieved to learn about the death of Vitaly Churkin. The head of state highly estimated Churkin’s professionalism and diplomatic talents,” spokesman Dmitry Peskov said, according to the agency.

Russia’s foreign ministry called Churkin an “outstanding” diplomat and expressed condolences to his friends and family. Spokeswoman Maria Zakharova said in a Facebook post that Churkin was “an extraordinary person. A bright man. We have lost a dear one.”

His death, the day before his 65th birthday, stunned officials at the U.N.’s headquarters.

“Our thoughts go to his family, to his friends and to his government,” said U.N. deputy spokesman Farhan Haq, who heard the news from reporters as it circulated during a daily briefing.

Diplomatic colleagues mourned Churkin as a powerful and passionate voice for his nation, with both a deep knowledge of diplomacy and a large and colorful personality.

Calling Churkin a “diplomatic maestro and deeply caring man,” former U.S. Ambassador to the U.N. Samantha Power said on Twitter that Churkin had done all he could to bridge differences between the U.S. and Russia.

French U.N. Ambassador Francois Delattre, too, said he and Churkin had “always worked together in a spirit of mutual respect and personal friendship,” despite their divides. One of Delattre’s predecessors, Gerard Araud, now French ambassador to the U.S., recalled Churkin as “abrasive, funny and technically impeccable.”

Britain’s U.N. ambassador, Matthew Rycroft, tweeted that he was “absolutely devastated” to hear of the death of Churkin, “a diplomatic giant and wonderful character.”

Churkin was previously ambassador at large and earlier served as the foreign ministry spokesman. Churkin had a doctorate in history and was a graduate of the Moscow State Institute of International Relations. And he was a child actor in what was then the Soviet Union.