Vitaly Churkin, the Russian ambassador who represents the Russian Federation in the United Nations is dead at 64. Russian officials say his death in New York, while at work on Monday, was sudden. ABC news reports:

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.

Other news outlets are reporting Mr. Churkin may have died of a cardiac arrest. One thing is known — Vitaly Churkn was very admired at the United Nations. The ambassador is said to have been “Moscow’s great champion” at the U.N. and is known for his sharp wit and repartee — especially with “American and Western counterparts.”

Former President Obama's National Security Advisor and former @USUN Ambassador, Susan Rice said she was shocked by the news, adding Mr. Churkin was highly effective and very funny.

x I'm shocked and deeply saddened by this news. Vitaly was a huge force at the UN. Smart, committed, highly effective and very funny. https://t.co/VTKJmolhY2 Ã¢ÂÂ Susan Rice (@AmbassadorRice) February 20, 2017

The former U.S. Ambassador to the United Nations, Samantha Power, expressed her condolences also on Twitter following the news of Mr. Churkin’s death calling him a deeply caring man.

x Devastated by passing of Russian UN Amb Vitaly Churkin.Diplomatic maestro &deeply caring man who did all he cld to bridge US-RUS differences Ã¢ÂÂ Samantha Power (@SamanthaJPower) February 20, 2017

Matthew Rycroft, the British ambassador to the UN, called Mr. Churkin's death the loss of a "diplomatic giant."

x Absolutely devastated to hear that my friend & colleague Vitaly Churkin has died. A diplomatic giant & wonderful character. RIP Ã¢ÂÂ Matthew Rycroft (@MatthewRycroft1) February 20, 2017

Condolences continue to come in from ambassadors diplomats from around the world. This news story is still developing. In a recent interview with CBS News and two other news organizations, Churkin said U.S.-Russia relations were “probably the worst since 1973.”

“The big distinction between the Cold War and the current climate is that during the Cold War, the attitude at the U.N. was that Russia would never vote with the U.S.;” now, he said, the two nations cooperate in several areas and worked with the U.S. and other nations to find a consensus candidate to be the next Secretary General.

Reuters reports Mr. Churkin first came to prominence as foreign ministry spokesman for the Soviet Union from 1990, until the collapse of the superpower the following year.

Despite the pressure of events, he appeared to revel in the attention of the Western correspondents who mobbed him at briefings, and was happy to respond to them at length in fluent English. He went on to serve as deputy Russian foreign minister and ambassador to Belgium and then to Canada, eventually moving to the U.N. in 2006.

The deputy spokesman for the U.N. secretary-general's office, Farhan Haq, said he was stunned, adding Mr. Churkin had been a regular presence at the United Nations. “ Our thoughts go to his family, to his friends and to his government."