Russia's ambassador to the United Nations, Vitaly Churkin, who for years fended off western criticism and defended Moscow's actions in Ukraine and Syria, has died in New York, aged 64.

Life of a career diplomat Churkin had served as foreign ministry spokesman in the early 1990s and as special envoy to the former Yugoslavia. Growing up in Moscow, he dabbled in acting in his early teens, notably in two films about Soviet founding father Vladimir Lenin. He graduated from the prestigious Moscow Institute of International Relations and began his career at the foreign ministry as a translator before working at the Soviet embassy in Washington in the 1980s. Given his long posting at the UN - previously held for a decade by Russia's current Foreign Minister Sergey Lavrov - Churkin joked in a recent interview that his stint was surpassed only by the envoy from Turkmenistan. He is survived by his wife Irina, son Maxim and daughter Anastasiya.

Churkin collapsed while at work at the Russian mission to the UN on Monday morning and was taken to a Manhattan hospital, apparently suffering from heart problems, diplomatic sources told AFP news agency.

In a statement announcing his death, the foreign ministry in Moscow described him as an "outstanding diplomat".

Kremlin spokesman Dmitry Peskov said President Vladimir Putin "highly valued the professionalism and diplomatic talent of Vitaly Churkin" and offered condolences, Interfax reported

Russian foreign ministry spokeswoman Maria Zakharova paid tribute, writing on Facebook: "A great diplomat. An extraordinary personality. An outstanding individual. We have lost someone very dear."

News of his death was met with shock at UN headquarters where Churkin, who would have turned 65 on Tuesday, had been a towering presence for a decade.

UN Secretary-General Antonio Guterres said Churkin had served "with distinction through some of the most challenging and momentous periods of recent history".

Guterres described him as a "forceful presence on the Security Council", a "uniquely skilled diplomat, a powerful orator with great wit and a man of many talents and interests".

Diplomats at a UN meeting observed a moment of silence and a tribute to him was planned at the Security Council on Tuesday.

Petr Iliichev, Russia's deputy UN ambassador, said Churkin was worked "until his last moments".

"His whole life was dedicated to defending the interests of Russia," Iliichev said. "He was on the frontline ... We've lost a prominent diplomat, a strong negotiator, a wonderful individual, a teacher."

V.Churkin passes away... Great loss for Russia. His memory will live on in our hearts forever https://t.co/pj4UdxmWUM pic.twitter.com/j2AS8AIT0W — Russian Mission UN (@RussiaUN) February 20, 2017

UN spokesman Farhan Haq, who was informed of Churkin's death during a daily briefing, offered his condolences.

"He has been such a regular presence here that I'm actually quite stunned," Haq said.

Western rift

A career diplomat born in Moscow who studied English from a young age, Churkin had been UN ambassador since April 2006, after serving as Russian ambassador to Canada and to Belgium.

Recently, relations between Russia and the West have soured, culminating with a major rift over Moscow's support for separatists in east Ukraine and its military intervention in Syria.

In his final months, Churkin clashed repeatedly with then-US ambassador Samantha Power over the bloodshed in Syria's Aleppo, staunchly defending Moscow's view that the Syrian government was waging all-out war against "terrorists".

Russia resorted to its veto six times to block action on Syria.

Power tweeted that she was "devastated" and described Churkin as a "diplomatic maestro" who did all he could to bridge US-Russian differences.

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

Power's successor, Nikki Haley, who arrived less than a month ago, said Churkin had "showed himself to be a gracious colleague".

"We did not always see things the same way, but he unquestionably advocated his country's positions with great skill," said Haley in a statement.

Francois Delattre, Churkin's French counterpart, said he was "one of the most talented diplomats" and "an exceptional representative of Russia.

Matthew Rycroft, Britain's ambassador to the UN, tweeted that he was "absolutely devastated", describing Churkin as "a diplomatic giant & wonderful character".