According to a flurry of communications on the relationship, there are also serious allegations of ''shared, personal business interests'' in Russian gas projects worth billions - which both leaders deny.

Mr Berlusconi was due visit Mr Putin's Black Sea dacha in Sochi last night. Plans for the visit emerged just hours after the publication of the damaging WikiLeaks cables.

Mr Berlusconi had been due to attend a two-day Italo-Russian summit that included a lunch with the President, Dmitri Medvedev, tomorrow. But, according to the Ansa news agency, Mr Putin will also fly to Sochi to attend the lunch.

Before leaving, Mr Berlusconi said: ''The US know full well that I have no interests with any countries, and no personal interests, and that I have only the interests of Italy and my country at heart.''

The cables suggest Mr Berlusconi's negotiation of generous conditions for the Italian oil and energy company Eni with the Russian firm Gazprom is related to the Italian leader supporting Russian energy projects rather than those of Western nations, a development the US believes endangers their own energy interests.

And US diplomats believe Mr Berlusconi is immune to political influence, taking personal control of decisions relating to Russia, while banning Italian diplomats from involvement.

The cables record that when the former US vice-president Dick Cheney asked about Russo-Italian relations, the Italian Foreign Minister, Franco Frattini, apparently just shrugged his shoulders - implying he had nothing to say about Russia.

The former US ambassador to Italy, Ronald Spogli, in a nine-page memo written last year, suggested that suspicions about an arrangement between the two leaders is spoken of openly by foreign diplomats.

''They believe that Berlusconi and his cronies are profiting personally and handsomely from many of the energy deals between Italy and Russia,'' Mr Spogli wrote.

''The Georgian ambassador in Rome has told us that the Georgian government believes Putin has promised Berlusconi a percentage of profits from any pipelines developed by Gazprom in co-ordination with Eni.''

The cables, the Italian newspaper La Repubblica reported, state that meetings between the Russian and Italian leaders are accompanied by ''luxurious gifts''. Enmeshed in the relationship, the cables say, is Valentino Valentini, an Italian parliamentarian who is Mr Berlusconi's principal adviser on Russia. The ''somewhat shadowy figure'' speaks Russian and, according to Mr Spogli, visits Russia several times a month, often turning up at Mr Berlusconi's side.

''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,'' he wrote.

The Americans' unease is ongoing. After a visit to the Italian Prime Minister's country home in Lombardy on New Year's Day this year by Mr Spogli's successor, David Thorne, Mr Berlusconi appeared cheered to have company as he recuperated from a facial injury.

The American diplomat observed that Mr Berlusconi did not ask the US for a single favour and, Mr Thorne wrote, he appeared to want to be a good partner to the Americans.

But the visit was interrupted by a telephone call: the Russian PM wanted to speak with Il Cavaliere.

Out went the US ambassador; Russia was more important.

According to the German newspaper Der Spiegel's account of the cables, this vignette is indicative of the complexity of the US's relationship with Mr Berlusconi, a media tycoon, who declares himself to be pro-American but whose professional and personal life makes his leadership ''unorthodox''.

''Sex scandals, criminal investigations, family problems and financial concerns appear to be weighing heavily on Berlusconi's personal and political health as well as on his decision-making ability,'' the cables note.

The cables also show that along with a penchant for Mr Putin himself, Mr Berlusconi has a soft spot for his parties - as wild celebrations in Italy have become too politically risky.

One cable claimed that in October last year, Mr Berlusconi snubbed a state visit to Italy by King Abdullah of Jordan because he wanted to pursue ''private fun over statecraft'' as ''he was husbanding his flagging energies for a blow-out party at Putin's private dacha'' at Sochi.

with Guardian News & Media