Shareholders in Yukos are turning to international legal action to win compensation from the Russian authorities over the sharp drop in the Russian oil group's value.

Tim Osborne, a director of Menatep, which controls 60 per cent of Yukos, said he had filed a complaint against the Russian administration under the terms of the Energy Charter, a treaty ratified by Russia and designed to protect investors.

The treatment of Yukos by Russian authorities is also starting to affect the country's relations with Sweden, home to some of the biggest portfolio investors in the Moscow stock market.

Swedish officials have raised the possibility of investors suing the Russian government over their Yukos losses. They also point to investors' fears that the debacle could slow Russia's fur ther integration in the world economy.

Menatep's move is the first aggressive attempt by Yukos investors to seek redress for the damage caused by the company's plummeting share price as a result of attacks by Russian tax authorities that are believed to be politically motivated. Yukos shares have fallen 82 per cent from their peak last year to $2.90 yesterday.

The news came on the day Yukos said it would hold an extraordinary general meeting on December 20 to seek sharehold ers' views on filing for bank ruptcy in the wake of additional tax claims this week bringing the total sought for 2000-02 to $17bn (€13.39bn).

The Energy Charter compensa tion claim is being made by Hul ley and Yukos Universal, the Cyprus-based vehicles through which Menatep holds its Yukos shares.

Both Cyprus and Russia are parties to the treaty, which seeks to protect investors by offering fair market compensation for any loss or expropriation of assets.If the Russian state fails to reach an amicable agreement within three months, Menatep has the right to seek international arbi tration.

Menatep is the vehicle through which Mikhail Khodorkovsky, Yukos' former chief executive and largest shareholder, who is on trial for fraud and tax evasion in Moscow, controlled the com pany along with a small group of partners.

Separately, Sven Hirdman, Sweden's ambassador to Moscow, has expressed concern in letters to German Gref, Russia's econ omy minister, and Mikhail Zura bov, the pensions minister.

“Swedish investors have been informed of a number of possible breaches of due process of law and a general lack of goodwill by the relevant authorities,” one of the letters says.

“The only option for many of these investors would be to seek recourse through international courts for loss of investment,” the letter says.