The United States was aware of Bulgarian Prime Minister Boyko Borisov’s alleged ties to the mafia and shady businessmen before he was elected in 2009, according to a leaked diplomatic cable yesterday.

In the 2006 cable, released via WikiLeaks and a Bulgarian offshoot Balkanleaks, Washington’s ambassador to Bulgaria at the time, John Beyrle, wrote about Mr Borisov’s alleged “close social and business ties to influential mafia figures” and warned the United States must “never forget who we’re dealing with”.

The cable was written at a time when Mr Borisov was still mayor of Sofia, but harboured much bigger political ambitions.

Mr Borisov, a former bodyguard and fire-fighter, was elected Prime Minister in 2009 and is still hugely popular and widely expected to run in the upcoming presidential election in the autumn.

Back in 2006, Mr Beyrle described him as “an unpredictable individual with unbridled political ambition and an apparently bright future in Bulgarian politics.”

Nevertheless, it was precisely Mr Borisov’s ego that “may provide our greatest leverage over him – he craves international attention and particularly covets US approval,” the cable stated.

“We must continue to walk a fine line between being used by Mr Borisov’s publicity machine and alienating an exceptionally popular and seemingly pro-American politician who may emerge as Bulgaria’s next leader.”