Updated

MOSCOW -- Gevork Vartanian, a former Soviet intelligence agent who helped derail a Nazi plot to assassinate allied leaders at a 1943 conference in Tehran, has died. He was 87.

Russia's Foreign Intelligence Service, a top KGB successor agency, said Vartanian died of an unspecified illness Tuesday.

President Dmitry Medvedev sent condolences to Vartanian's widow, who worked together with him on intelligence missions abroad. Medvedev praised Vartanian on Wednesday as a legendary figure who participated in "brilliant special operations which became part of history of the nation's foreign intelligence."

The Foreign Intelligence Service said Vartanian, whose father was a Soviet intelligence agent based in Tehran, began working for Soviet intelligence when he turned 16. He played a role in foiling a Nazi plot to assassinate Soviet leader Josef Stalin, U.S. President Franklin D. Roosevelt and British Prime Minister Winston Churchill when they held a conference in Tehran in November 1943.

The Foreign Intelligence Service, which goes under its Russian acronym SVR, said that acting on orders from Moscow, Vartanian joined a British intelligence school in Tehran and obtained information about its graduates sent to the Soviet Union, allowing Soviet authorities to catch them.

The SVR said that Vartanian and his wife worked as intelligence agents in several countries between the early 1950s and 1986, but didn't name them.

The ITAR-Tass news agency said they worked in Iran, Italy, France and Greece among other nations.