Eni, the Italian energy group, has become the first foreign company to buy part of the former Yukos empire in Russia by claiming victory yesterday in a near-£3 billion auction of oil and gas assets.

The group immediately said that it would be handing over the bulk of the interests to Gazprom, the Kremlin-controlled gas giant, in an agreement criticised by Yukos shareholders.

The deal will mean that Gazprom takes a minimum 51 per cent stake in the former Yukos gas production companies Arcticgas and Urengoil and its energy arm Neftegaztechnologia.

Under a separate call option, it will also prise back a 20 per cent stake in its subsidiary GazpromNeft, which Eni won in the auction. GazpromNeft is the former Sibneft oil group that Roman Abramovich, the Chelsea Football Club owner, sold two years ago.

Yukos shareholders said that the arrangement showed that the auction had been little more than a sham. They claimed that President Putin and Romano Prodi, the Italian Prime Minister, had spoken on the telephone on Monday night in what appears to have been a negotiation over yesterday’s deal.

Robert Amsterdam, a lawyer representing Mikhail Khodorkovsky, the former Yukos owner, told The Times: “It looks like Eni is acting as a front for Gazprom.”

Despite the controversy, analysts said that the deal was a significant victory for Eni, which will add more than one billion barrels of oil equivalent to its reserves.

Enel, its rival Italian electricity group, will also benefit. It had a 40 per cent stake in the Eni subsidiary — EniNeftegaz — declared to be the auction’s official winner.

Paolo Scaroni, Eni’s chief executive, insisted that the deal marked his group’s entrance on to Russia’s lucrative upstream oil and gas sector as a “major player . . . This transaction, which is in the context of a fruitful ongoing relationship between Italy and Russia, underlines the value of a strategic partnership with Gazprom.”

The auction was the second in a series of sell-offs that mark the final dismemberment of the Yukos group, Russia’s biggest oil producer until four years ago. The company was declared bankrupt last year under a massive back tax-bill.

Supporters claimed that the tax investigation was a punishment for Khodorkovsky’s political ambitions. He is in a Siberian prison, serving an eight-year prison sentence for tax evasion and fraud.

Rosneft, Russia’s state-controlled oil company, won the first auction last week when BP’s Russian venture TNK-BP pulled out after just ten minutes of bidding.

Industry experts argued that the Kremlin had wanted foreign involvement in the auction process to add credibility.

Under Mr Putin, Russia has gradually been reclaiming majority control in its oil and gas assets. However, Roland Nash, head of research at Renaissance Capital, said yesterday: “It’s not all one-way traffic. There is a role for foreign institutions to invest in the Russian hydrocarbons sector — just under Russia’s terms.”

What £3bn can buy

What Eni bought:

— 100 per cent of the Yukos gas production firms Arcticgas and Urengoil, as well as 100 per cent of the energy unit Neftegaztechnologia

— 20 per cent of GazpromNeft, formerly known as Sibneft. Produces over 900,000 barrels of oil a day and has a refining capacity of 690,000 barrels

— Various minor assets that will be sold or liquidated

— Goldman Sachs said Eni’s share of reserves from the deal will be one billion barrels of oil equivalent, to replace 190 per cent of Eni’s output in 2007

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