Iranian Foreign Ministry Spokesman Bahram Qassemi extended condolences with Russian nation and government over death of Russian ambassador to the United Nations, Vitaly Churkin.
He expressed sympathy with his family as well as Russian state over the loss.
On Monday, Russia said Churkin "died suddenly” in New York, just a day before his 65th birthday.
The Russian Foreign Ministry said in a statement that Churkin died after being taken ill at work, but gave no details on the circumstances of his death.
"We'd like to express our sincere condolences to Vitaly Churkin’s family,” the Russian Foreign Ministry said but declined to comment on reports that Churkin had been taken to hospital shortly before his death.
Earlier, Russia's deputy UN ambassador, Vladimir Safronkov, told The Associated Press that Churkin was rushed to a hospital in New York, where he died.
His cause of death was not immediately known, but a law enforcement official said he had suffered a cardiac arrest before being transferred to hospital.
Following the announcement, tributes and messages of condolences began to pour in.
President Putin offered his condolences to Churkin’s family and to all Russian diplomats.
Kremlin spokesman Dmitry Peskov also said "the head of state highly valued Churkin’s professionalism and diplomatic talent.”
Russian Foreign Ministry spokeswoman Maria Zakharova also described him as "a great diplomat of our age,” saying the news of his death was "completely shocking.”
UN General Assembly members also stood for a moment of silence in memory of the late diplomat.
"We’ve lost one of the most respected and influential members of the UN family,” said UN General Assembly President Peter Thomson.
Meanwhile, Farhan Haq, deputy spokesman for the UN Secretary General's office, offered his condolences.
"We mourn Ambassador Churkin. He has been such a regular presence here that I am actually quite stunned. Our thoughts go to his family, to his friends and to his government,” he said.
Before being appointed to represent Russia at the UN on May 1, 2006, Churkin was Ambassador at Large at the Ministry of Foreign Affairs of the Russian Federation between 2003 and 2006.
He was Russia’s Ambassador to Canada from 1998 to 2003, Ambassador to Belgium and Liaison Ambassador to NATO and the Western European Union (WEU) between 1994 and 1998.
Churkin also served as Deputy Foreign Minister and Special Representative of the President of the Russian Federation to the talks on Former Yugoslavia (1992-1994).