The United States expressed disappointment Thursday over the Russian government's de facto takeover of the main asset of the giant Yukos oil company. The State Department said it could "negatively impact" Russia's role in the global economy.

The United States has been troubled by the Russian government's handling of the Yukos affair since the company's chief, Mikhail Khodorkovsky, was forced to resign and jailed on fraud charges more than a year ago.

Now, with the company's main production unit having been absorbed by the state run Rosneft oil firm, the Bush administration is expressing renewed concern.

At a news briefing, State Department Deputy Spokesman Adam Ereli said the effective re-nationalization of the oil giant calls into question stated free-market commitments by the government of President Vladimir Putin. "Obviously, we're disappointed in the way this case has been handled. We certainly don't think it's been disposed of in a transparent or open way. We think this sends the wrong signals to foreign investors and could negatively impact Russia's role in the global economy," he said.

Mr. Ereli said the United States wants to see trade and investment in Russia "flourish." He said it is thus important that the Putin government acts to assure those watching the Russian economy that the "weaknesses and questions" raised by the Yukos affair are addressed "in ways that restore confidence in Russian institutions."

Under questioning, Mr. Ereli denied that in the interest of harmony with Mr. Putin, the U.S. administration has soft-pedaled criticism of the Yukos affair and particularly the incarceration of Mr. Khodorkovsky on what many observers say are trumped-up charges. "I think we've said that the way this is handled raises serious concerns about the way the rule of law is applied in Russia and the way that justice is perhaps politically and selectively applied. And we have called upon Russian institutions to act in ways that address those concerns," he said.

Mr. Ereli said it is important for the United States to have the kind of relationship with Moscow that "allows you to engage."

He said while the two countries work together in areas where they have mutual interests, administration officials from President Bush on down have been "very clear and outspoken" in talks with their Russian counterparts about matters of U.S. concern.

The spokesman also rejected a suggestion by President Putin at a news conference Thursday that the United States has sought to isolate Moscow.

He said the Bush administration sees Russia as a valued and important member of the international community and that its actions demonstrate that quite clearly.

Mr. Ereli cited, among other things, work with Russia in the international "Quartet" on the Middle East and the six-party talks on North Korea's nuclear program, and said isolating Russia is, in his words, "contrary to our approach and interests."