Soviet dictator Joseph Stalin spied on 'Chairman' Mao Zedong and other world leaders in the 1940s by analysing their excrement to construct psychological portraits, a former Soviet agent has claimed.

Former Soviet agent Igor Atamanenko claims to have uncovered this unusual project while doing research in the archives of the Russian secret services. The secret lab was headed by Stalin's henchman Lavrenti Beria.

Under this, special toilets were allegedly installed for the Chinese Communist Party leader Mao to use when he visited Moscow for 10 days in December 1949.

During those 10 days, Mao was piled with food and drink and his waste products whisked off for analysis.

The toilets were not connected to sewers, but collected his waste in secret boxes to be taken to the lab and studied for varying levels of potassium and amino acids, which were thought to aid psychological profiling, the BBC reported.

Once Mao's stools had been scrutinised and studied, Stalin reportedly poo poo-ed the idea of signing an agreement with him, the report said.

"In those days the Soviets didn't have the kind of listening devices which secret services do today," Atamanenko told the Komsomolskaya Pravda newspaper.

"That's why our specialists came up with the most extravagant ways of extracting information about a person."

"When I contacted Atamanenko, he told me what the Soviet scientists had been looking for in faeces.

"For example, if they detected high levels of amino acid Tryptophan," he explained, "they concluded that person was calm and approachable."

But a lack of potassium in poo was seen as a sign of a nervous disposition and someone with insomnia."

The Pravda reports that Stalin's successor, Nikita Khrushchev, scrapped the project and closed the laboratory.

When asked if it could confirm Stalin's secret stool project, Russia's Federal Security Service told the BBC: "We cannot comment on this story."