James Mulva's comments came during a trip to Lithuania

The firm's boss James Mulva made the comments during a visit to meet the Lithuanian government.

The facility is currently majority owned by Russian oil firm Yukos, which is said to be keen to sell to help pay its giant $27.5bn (�15.2bn) tax bill.

However, the Russian government may try to block any sale.

Russian partnership

Mazeikiu Nafta is currently 53.7%-owned by Yukos and 40.6%-owned by the Lithuanian government.

Yukos' stake is estimated to be worth about $1bn.

The Lithuanian government is also said to be interested in selling part of its stake.

Mr Mulva said:"It is possible that over some period of time we could acquire ownership interests in the refinery."

ConocoPhillips is the largest oil refiner in the US

Any purchase is likely to involve Conoco's Russian partner Lukoil, he said, adding that Lukoil's involvement would secure a ready supply of oil to refine.

Sale freeze?

However, the Russian Justice Ministry said on Wednesday that it had called on the Lithuanian and Dutch governments to freeze any Yukos assets in their countries.

"It must be said that Yukos is not making active efforts to pay down this debt," said a statement for the ministry.

While the Kremlin insists Yukos illegally abused tax loopholes, the company's jailed boss Mikhail Khodorkovsky and his supporters believe the tax claim is politically motivated.

If Yukos does proceed with a sale, other companies are also likely to be interested as well.

The UK's BP and Russia's Gazprom are two other firms said to be interested in the facility.

ConocoPhillips is the biggest oil refiner in the US and the fifth largest worldwide.