Image copyright AP Image caption Mao Zedong (L) and Josef Stalin (R) were the two most powerful leaders in the communist world at the time (two photos have been merged together to create this image)

A former Soviet agent says he has found evidence that Joseph Stalin spied on Mao Zedong, among others, by analysing excrement to construct psychological portraits.

By the sound of things, it was a top secret and rather smelly experiment.

According to Russian newspaper reports, in the 1940s Stalin's secret police had set up a special department to get its hands on people's faeces.

The ambitious aim: to analyse samples of foreign leaders' stools.

In other words, espionage via excrement.

'Most extravagant'

It is former Soviet agent Igor Atamanenko who claims to have uncovered this unusual project, while doing research in the archives of the Russian secret services.

"In those days the Soviets didn't have the kind of listening devices which secret services do today," he told the paper.

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

Mr Atamanenko says it was Stalin's henchman Lavrenti Beria who was put in charge of the secret laboratory.

When I contacted Mr 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.

Image copyright AFP/Getty Images Image caption Special toilets were reportedly installed for Mao Zedong while he was in Russia so his faeces could be harvested and analysed (this photo is from 1961)

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

Mr Atamanenko claims that in December 1949, Soviet spies used this system to evaluate the Chinese leader Mao Zedong who was on a visit to Moscow. They had allegedly installed special toilets for Mao, which were connected not to sewers, but to secret boxes.

For 10 days Mao was plied with food and drink and his waste products whisked off for analysis. Once Mao's stools had been scrutinised and studied, Stalin reportedly poo poo-ed the idea of signing an agreement with him.

'I am here to do more'

Extract from The Coldest Winter by journalist and historian David Halberstam:

When Mao first arrived in Moscow, he announced that China looked forward to a partnership with Russia, but he emphasised as well that he wanted to be treated as an equal.

Instead he was being taught a lesson each day. He had become, in Ulam's words, ''as much captive as guest".

As such, he shouted at the walls, convinced that Stalin had bugged the house: "I am here to do more than eat and shit."

One of Russia's most popular daily newspapers, Komsomolskaya Pravda reports that Stalin's successor, Nikita Khrushchev, scrapped the project and closed the laboratory.

I contacted Russia's Federal Security Service, the FSB, to ask if it could confirm Stalin's secret stool project. However, the FSB had considerably less to say on the matter than Mr Atamanenko:

"We cannot comment on this story," came the reply.