UNITED NATIONS, Feb. 20 (Xinhua) -- The sudden death of Russian Ambassador to the UN Vitaly Churkin Monday stunned the diplomatic community, staff of the UN secretariat and reporters.

The 64-year-old veteran diplomat was the longest-serving ambassador on the 15-member UN Security Council, where he was known for his quick-witted debating skills and good humor.

Churkin has been Russian permanent representative since 2006, who succumbed after an apparent heart attack in New York on the eve of his 65th birthday.

President of the 71st session of the UN General Assembly Peter Thomson said that he was "greatly saddened" at the news of the passing of the Russian ambassador.

Thomson, who described the late Russian envoy as a "dear friend," said in a statement by his spokesman that "the Russian Federation and the United Nations have lost a true son and a great international intellect."

Members of the General Assembly stood for a moment of silence in memory of Churkin before an informal briefing on Sustainable Development Goals held in the Trusteeship Council Chamber.

"The members of the Security Council were deeply saddened to learn of the death of Ambassador Vitaly Churkin," an official statement issued late Monday said.

"The members of the Security Council expressed their deep condolences to the family of the Ambassador, the Government and the people of the Russian Federation," it concluded.

UN Secretary-General Antonio Guterres was traveling in the Middle East and Europe so there was no immediate formal response, but, Farhan Haq, the deputy UN spokesman, was visibly and audibly surprised by an initial report of Churkin's death.

"He has been such a regular presence here that I am actually quite stunned," Haq said. "Our thoughts go to his family, to his friends and to his government."

The Russian foreign ministry said in a formal statement issued in Moscow, "A prominent Russian diplomat has passed away while at work. We'd like to express our sincere condolences to Vitaly Churkin's family."

Meanwhile, most reactions to the sudden death of Moscow's envoy to the world organization came in a modern-day style of Twitter messages.

U.S. Ambassador to the UN Nikki Haley, Churkin's traditional rival, issued a brief statement.

"In my short time at the United Nations, Ambassador Vitaly Churkin showed himself to be a gracious colleague," she tweeted. "We did not always see things the same way, but he unquestionably advocated his country's positions with great skill."

"Devastated by passing of Russian UN Amb Vitaly Churkin. Diplomatic maestro & deeply caring man who did all he cld to bridge US-RUS differences," tweeted Samantha Power, former U.S. Ambassador to the world organization.

"Absolutely devastated to hear that my friend & colleague Vitaly Churkin has died," tweeted British Ambassador Matthew Ryrcroft.

Ambassador Gerard Araud of France to the United States and former French permanent representative to the United Nations, tweeted of Churkin, "An extraordinary colleague during my 5y in the UNSC. Abrasive, funny and technically impeccable. Sincere condolences."

Born on Feb. 21, 1952 in Moscow, Churkin was ambassador-at-large at the Ministry of Foreign Affairs of the Russian Federation from 2003 to 2006. He was his country's ambassador to Canada from 1998 to 2003, and to Belgium from 1994 to 1998 before he represented Russia at the United Nations in 2006.