Russia's ambassador to the United Nations, Vitaly Churkin, dies The longtime Russian ambassador to the U.N., Vitaly Churkin, is dead.

 -- Vitaly Churkin, the longtime Russian ambassador to the United Nations, died today in New York, according to Russian officials.

Churkin died at 9:30 a.m. of cardiac arrest at the Russian Mission to the U.N., which is located on Manhattan's Upper East Side, according to the NYPD and Russian officials.

He was pronounced dead at New York Presbyterian Hospital, according to the NYPD.

In a short statement calling Churkin an “outstanding” diplomat, the Russian Foreign Ministry said that Churkin died today, the day before his 65th birthday.

Churkin had served as the Russian ambassador since 2006.

He had a reputation as a master of U.N. procedure, and frequently jousted with his American counterparts over Georgia, Crimea, Iran, Iraq, Libya and Ukraine.

Most recently, Churkin drew notice for verbally sparring with American diplomat Samantha Power, who served as the U.S. ambassador to the United Nations from 2013 to 2017, with the second Obama administration.

After Power attempted to shame Churkin for the massacre of civilians in Aleppo, Syria, Churkin mockingly compared her to "Mother Teresa."

Despite their sometimes prickly encounters, Power said today she was devastated by Churkin's loss, and described him as a "diplomatic maestro" and a "deeply caring man" in a tweet.

Matthew Rycroft, Britain's U.N. ambassador, called Churkin a "pillar" in a tweet, and offered condolences to his family and colleagues.

This is a developing story. Please check back for updates.

ABC News' Aaron Katersky contributed to this report.