In the early 2000s, intelligence experts at the US National Security Agency (NSA) successfully intercepted calls from the phone of a Russian crime boss in order to probe suspected links with Vladimir Putin, it has been revealed.

The news emerged from recently disclosed (16 May) documents leaked by former NSA-contractor Edward Snowden, published by The Intercept, and revealed how one request from the US State Department urged the agency to investigate links between the controversial head of state and the notorious Tambov crime syndicate.

"State wanted to learn whether there were any links between the St Petersburg syndicate and Russian President Vladimir Putin, who had been deputy mayor of St Petersburg in the mid-1990s," said the 2003 document from an internal NSA newsletter called SIDToday, produced by the agency's Signals Intelligence Directorate.

The surveillance target was a former Russian mafia kingpin called Vladimir Kumarin, who later changed his name to Vladimir Barsukov. He was imprisoned in Russia in 2009 for 14 years after being charged with crimes including extortion, fraud and attempted murder.

While interest in Kumarin was expected in Russia, the leaked NSA document reveals US authorities were also curious about his close acquaintances during the time running the syndicate in the 1990s.

As such, the release, which is labelled TS/SI for Top Secret, provides previously unknown insight into how the NSA – in its own words – "attacks" new intelligence targets from scratch. While initially, the document admits that signals intelligence analysts "had their work cut out for them" as the agency lacked a phone number or a sample of the targets voice, it said the operation was eventually successful after "many months of target development".

"The Office of Crime and Narcotics (OCN) is now issuing SIGNT reports based on intercept of Kumaran's telephone," wrote the chief of NSA's Transnational Organised Crime Branch at the time. "We not only acquired Kumarim's phone number, but also gained more insights into his organisation and activities."

The newsletter added: "The identification and collection of Kumarin's phone number was made possible by the efforts of OCNs [REDACTED] who worked with Math Research Group analysts to produce contact chaining charts and collection manager to optimise collection."

Unfortunately, the internal NSA report does not disclose if the agency found any links between Putin and the activities of Kumarin or the exact information gleaned from the interception probe.

Allegations of corruption

Last year, a number of officials with reported links to Putin were named in a high-profile Spanish investigation that examined how members of the Tambov crime syndicate expanded into Spain in 1996, while Putin was the deputy mayor of St Petersburg.

The report, which was the result of roughly a decade of investigative work on behalf of Spanish authorities, alleged links between Tambov-led criminality and "top law-enforcement officials and policymakers" in Russia.

As previously reported, Putin was mentioned by name three times in the document however his spokesman, Dmitry Peskov, denounced the report's findings at the time and said the allegations were "beyond the realm of reason".

Meanwhile, former crime leader Kumarin was also referenced during the recent probe into the death of former Russian spy Alexander Litvinenko, which also ended up with allegations of the "strong probability" of Kremlin involvement.

In the investigation after his death, it emerged that Litvinenko, a former KGB spy, claimed in a report that "Putin's enforcer" Viktor Ivanov had close ties with crime gangs involved in cocaine smuggling. Ivanov, authorities claimed, was also closely involved with St Petersburg crime and had worked alongside Vladimir Kumarin during his time leading the gang.