The United States has raised concerns about the arrest of Russian oil tycoon Mikhail Khodorkovsky.
Mikhail Khodorkovsky is said to be worth $8bn
US ambassador in Moscow, Alexander Vershbow said the arrest could raise doubts for foreign investors.
Mr Vershbow told Interfax news agency "recent events provoked questions about whether or not Russian legislation is being applied selectively".
Mr Khordorkvsky, head of oil firm Yukos was charged with offences including defrauding the state out of $1bn.
Mr Vershbow told the Russian news agency that Washington "was concerned about the escalation of tensions surrounding the Yukos company".
"I think that following these events foreign companies operating on the Russian market and prospective investors are going to have new doubts," he said.
"Of course, we cannot comment on the legal aspects of this case, but recent events have provoked questions about whether or not Russian legislation is being applied selectively."
Mr Vershbow said it was too early to comment on how the arrest may affect the plans of large US companies such as ExxonMobil and ChevronTexaco which have been showing an interest in buying shares in the merged company YukosSibneft.
Following the arrest and charges on Saturday a Moscow court ordered Mr Khodorkovsky, Russia's richest man, to be kept in prison.
Critics say the investigation into his company is an attempt by the Kremlin to assert its power over business tycoons and keep them out of Russian politics.
The company described the charges as "absurd".
Prosecutors argued that his detention was necessary because he had ignored a summons for questioning on Friday.
A Yukos spokesman said the company had received a summons, but they had written back to say that Mr Khodorkovsky was on a business trip and would be unable to appear.
Two Yukos executives are facing criminal charges, including Platon Lebedev, the group's chief financier, who is in jail waiting for trial on charges of defrauding a state company in 1994.
Earlier this month tax-evasion charges were filed against Vastly Sharkhnovsky, who is responsible for the auditing of operations.