The Kremlin on Wednesday paid tribute to a late Soviet intelligence officer it credits with helping foil a Nazi plot to kill Winston Churchill, Josef Stalin and Franklin Roosevelt, saying her career may have changed the course of history.

Goar Vartanyan, who died on Monday at the age of 93, was an undercover field operative for decades and allegedly helped thwart a plan backed by Adolf Hitler to assassinate the allied leaders at their first "Big Three" conference in Tehran in 1943.

Born in Armenia in 1926, Vartanyan moved to Iran in the 1930s where, at the age of 16, she joined an anti-fascist group led by her future husband, Soviet spy Gevork Vartanyan, that was tasked with ensuring security for the World War II conference.

The Soviet group, which had already unmasked more than 400 Nazi agents in Iran, identified a group of Nazi assassins ahead of the conference and arrested them, causing the plot, known as Operation Long Jump, to fail, Gevork Vartanyan has said.

"Without Goar Vartanyan and her husband Gevork, the history of our world could have been different. These are people who left their mark on the history of mankind," Kremlin spokesman Dmitry Peskov said on Wednesday.

The couple went on to work as undercover spies, known in Moscow as "illegals," in an array of countries from 1956 to 1986 after which Goar retired and began to train future agents, the Foreign Intelligence Service (SVR) said.

President Vladimir Putin, who himself served as a KGB officer in East Germany in the late Cold War, expressed his condolences to Vartanyan's family and relatives.

"Putin knew both Goar and her husband well... Goar visited Putin in the Kremlin, Putin visited her as a guest," Peskov told reporters.

Gevork Vartanyan, who was bestowed the title of Hero of the Soviet Union, the country's highest honor, died in 2012 at the age of 87 and was buried at a ceremony attended by Putin.

"He is a Hero of the Soviet Union! She is the heroine of all his achievements! He passed away first. She passed away today," the SVR said on Monday, announcing her death.

It referred to Goar by the code name "Anita" and Gevork as "Anri."

"Together with her husband... they were one of our most beautiful, charming and at the same time productive couples among our intelligence illegals," SVR chief Sergei Naryshkin said.