Boris Berezovsky, the Russian tycoon who has obtained political asylum in Britain, said he would sue his former protégé on the ground that he was pressured into selling his stakes in his main Russian assets after he fled the country. He accused Mr Abramovich, who is Britain's richest man, of acting on the orders of President Vladimir Putin.
Ironically, Mr Abramovich and Mr Berezovsky, his former business partner, became billionaires by benefiting from the selling of state assets at knockdown prices after the Soviet Union collapsed.
In an interview published yesterday in The Moscow Times, Mr Berezovsky said he and his business partner, Badri Patarkatsishvili, had each made less than $1bn (£570m) from the sale of their joint stakes in the Sibneft oil firm, Russian Aluminium, Russia's biggest aluminium maker, and the television channel ORT. He said this was significantly less than their market value.
He could not be reached for comment last night, but Mr Berezovsky told Ekho Moskvy radio from London that "between 2000 to 2004 ... I was deprived of my assets". He added: "Roman Abramovich was directly involved in this, and the organisers [included] Putin.
"At any rate, Abramovich said he was acting on orders from them, either I hand over what I own at a cheap price or they will take it away from me."
Mr Berezovsky explained that he was going to court to "create a precedent so people can defend their property rights". He added that he had decided to launch legal action in Britain because, unlike in Russia, British courts were "absolutely objective and will not submit to pressure from the British government or the Russian authorities".
John Mann, a spokesman for Mr Abramovich, said: "I won't comment on Mr Berezovsky's specific allegations, but the lawsuit seems far-fetched." In 1995, Mr Berezovsky and Mr Abramovich won control of Sibneft for just $100m, when it was estimated to be worth $1bn, in the controversial privatisation auctions known as "loans for shares".
Today, the market value of the oil company is $16.7bn and Mr Abramovich's Millhouse Capital owns 57.5 per cent of it.
The former business partners have become politically estranged since the privatisation of Russia's state sector, in which Mr Berezovsky built up an empire encompassing media, banks, cars, energy and a stake in the national airline Aeroflot.
He successfully applied for political asylum in Britain after he fled fraud charges in Russia, claiming he was being hounded by President Putin for his political activities. The media mogul is still wanted on fraud charges in Russia, and points to the nine-year jail term for fraud against another oligarch, Mikhail Khodorkovsky, as a warning to those engaging in political activities against Mr Putin's regime.
Mr Abramovich, 38, remains close to the Kremlin and is the governor of the Arctic region of Chukotka.
Mr Berezovsky's Kommersant business daily reported yesterday that Mr Abramovich was in the final stages of negotiations to sell a majority stake in Sibneft to the state-controlled gas monopoly, Gazprom.
Mr Abramovich has sold many of his Russian assets, and some investors are predicting that Sibneft would be sold as the state tightens its grip on the country's strategic assets in the wake of the trial of Mr Khodorkovsky, the head of the Yukos oil giant.