US diplomats have reported startling suspicions that Silvio Berlusconi could be “profiting personally and handsomely” from secret deals with the Russian prime minister, Vladimir Putin, according to cables released by WikiLeaks. Exasperated by Berlusconi’s pro-Russian behaviour, American embassy staff detail allegations circulating in Rome that the Italian leader has been promised a cut of huge energy contracts. The two men are known to be personally close, but this is the first time allegations of a financial link have surfaced.

Hillary Clinton’s state department in Washington sent a special request to the Rome embassy this year, asking for extra intelligence-gathering on the allegations about the men: “What personal investments, if any, do they have that might drive their foreign or economic policies?”. References to Berlusconi’s “financially enriching relationship” originated both from members of his own political party and from the hostile government of Georgia, according to the leaked cables.

The US ambassador in Rome, Ronald Spogli, first reported the claims in a series of dispatches in 2008-09. He said the prime minister had taken “single-handed” control of Italy’s dealings with Moscow, with the over-riding aim of pleasing the Russian leader.

Berlusconi acted as a “mouthpiece” for Putin, he reported, supporting him in public when Russia was being criticised.

Personal ties between the two were close, “with Putin’s family spending long visits at the Berlusconi family mansion in Sardinia at Berlusconi’s expense”. Berlusconi in turn has the rare privilege of being invited to Putin’s dacha in the Black Sea resort of Sochi for what the embassy speculated on one occasion would be a “blow-out party”. A contact in Berlusconi’s office told the embassy of “exchanges of lavish gifts”.

In January 2009, according to the leaked cables, Spogli wrote it was “hard to determine” the basis of the Berlusconi-Putin friendship. “Berlusconi admires Putin’s macho, decisive and authoritarian governing style, which the Italian PM believes matches his own”.

However, “contacts in both the opposition centre-left Partito Democratico and Berlusconi’s own PdL party … have hinted at a more nefarious connection. They believe that Berlusconi and his cronies are profiting personally and handsomely from many of the energy deals between Italy and Russia.”

Spogli continued: “The Georgian ambassador in Rome has told us that the government of Georgia believes Putin has promised Berlusconi a percentage of profits from any pipelines developed by Gazprom in co-ordination with ENI.”

The Italian energy conglomerate is partially owned by the Italian government. It works in close collaboration with state-controlled Gazprom, the energy giant which sells Russian gas and oil abroad.

Details of the allegations began to surface last night and were covered extensively by the Italian media this morning. Berlusconi denied the claims in the cables. Currently on a visit to Kazakhstan, he told the Ansa news agency: “The [United States] is quite clear that I have absolutely no interest in any other country; that there are absolutely no personal interests, and that I only look after the interests of the Italians and my country.”

But his denial did not satisfy opposition representatives who called for him to make a statement to parliament. Dario Franceschini, chief whip in the lower house of Italy’s biggest opposition group, the Democratic party, defied Bersluconi to deny the allegations. “We hope that those claims are not true. In any event, the prime minister should come to parliament to deny them next week,” he said.

Though the episode is not referred to in the cables, Berlusconi has publicly counselled Italians to buy ENI shares. On 10 October 2008, when the US credit crunch was at its height, Italy’s prime minister surprised financial observers.

According to Ansa, he told a press conference in Naples: “It’s the moment to buy ENI and [another Italian energy giant] Enel, both of which are undervalued.” In particular, he said, ENI “will this year make extraordinary profits”.

The private views of Georgian government sources were accurately relayed by the US embassy, according to Guardian inquiries. But neither Georgia nor the US record any concrete proof of their suspicion.

Spogli wrote: “Whenever we raise the issue of Russia and the P with our contacts in PdL, Berlusconi’s own party, they have usually pointed us to Valentino Valentini, a member of parliament and somewhat shadowy figure who operates as Berlusconi’s key man on Russia, albeit with no staff or even a secretary. Valentini, a Russian-speaker who travels to Russia several times a month, frequently appears at Berlusconi’s side when he meets other world leaders. What he does in Moscow during his frequent visits is unclear but he is widely rumoured to be looking after Berlusconi’s business interests in Russia.”

Elsewhere the US describes Valentini as Berlusconi’s “unofficial intermediary/bagman”.

In November 2008, the US ambassador sent a long cable to Condoleezza Rice, the then secretary of state, to prepare her for a meeting with the Italian prime minister.

“Berlusconi’s close personal (and, some suspect, financial) relationship with Putin has led him to champion unquestioningly every initiative the Kremlin has rolled out. Italy’s Russia policy is his personal game, one which he conducts on a tactical basis to gain the trust and favour of his Russian interlocutors. He consistently rejects the strategic advice of his demoralised, resource-starved and increasingly irrelevant foreign ministry in favour of his business cronies, many of whom are deeply dug into Russia’s European energy strategy.”