Moscow’s decisions to strip the oil company Yukos of its biggest asset and to give initial blessing to ConocoPhillips of the US to broaden its investment in Russia have drastically altered the most important strategic playing field of the big international oil companies.

The shift is most significant for ExxonMobil, the world’s largest energy group, which wants to make a large investment in Russia and had been actively seeking a significant stake in Yukos.

But with Mikhail Khodorkovsky, the former Yukos chairman, in jail and on trial for fraud and tax evasion, and the company’s main subsidiary Yuganskneftegas likely to go to a Russian buyer, the chance of ExxonMobil reaching a significant deal has dimmed, bankers and analysts said.

Meanwhile, President Vladimir Putin’s meeting with James Mulva last week and his blessing for possible further investment by Conoco-Phillips has raised the question among oil executives and the bankers who advise them of how many US companies the Kremlin will allow into Russia before closing the door on its most precious assets.

Mr Putin said: “I would very much like for the relationship between Russian and American business to develop more actively, particularly in such strategically important area as energy.”

He said he had been informed about ConocoPhillips’s plans in Russia. “Let me express the hope that this direction of your company will be as successful as what you have done before.”

Conoco in the past year has sought to broaden its partnership with Lukoil, Russia’s second largest oil company after Yukos, in the country’s Komi region. It is interested in buying the 7.6 per cent stake in Lukoil the government will auction off this year and has also been in talks over increasing its stake in the company by purchasing shares from its top management.

The meeting last week between Mr Mulva and Mr Putin was intended to demonstrate Russia’s openness to US business. But it was also meant to send an important message to the international community that it is the Kremlin and not the private owners of Russian oil companies that foreign companies must negotiate with. Indeed, one person close to Exxon said the Kremlin had made it clear to the Texas-based oil giant that the company had made a serious mistake by approaching Mr Khodorkovsky and trying to gain the Kremlin’s approval afterwards.

Exxon – with the help of Spencer Abraham, the US energy secretary – is also battling the Kremlin over an exploration licence the company holds in eastern Siberia. Moscow has threatened to re-open the rights to the fields to auction, saying Exxon has not invested enough in the project.

But ExxonMobil is not the only company that has watched with concern the changing investment climate in Russia.

Shifts in Russian policy also affect ChevronTexaco, the second largest US oil company, and Total of France, both of which are pursuing deals with Russian oil companies, as well as BP, which last year struck a 50/50 partnership with Russia’s TNK.

The international companies are also awash with cash, thanks to two years of high oil prices, and are looking to spend it. But with oil prices still above $40 a barrel, the Kremlin appears to have been emboldened to do things its way.