WASHINGTON -- A highly anticipated summit between U.S. President Barack Obama and Russian President Vladimir Putin could be hurt by Moscow's decision to grant temporary asylum to National Security Agency leaker Edward Snowden, the White House signalled after weeks of pressuring for his return to face prosecution.

"We are extremely disappointed that the Russian government would take this step despite our very clear and lawful requests in public and in private to have Mr. Snowden expelled," White House spokesman Jay Carney said Thursday.

Obama is scheduled to go to Russia in September for the Group of 20 economic summit in St. Petersburg and stop in Moscow for one-on-one talks with Putin.

Asked whether Obama would still travel to Moscow, Carney said, "We are evaluating the utility of a summit."

Snowden left the transit zone of a Moscow airport and officially entered Russia after authorities granted him asylum for one year, his lawyer said Thursday. The former intelligence contractor had been at the airport for more than a month since he arrived there from Hong Kong on June 23.

The U.S. had demanded that Russia send him home to face prosecution for revealing details about secret U.S. electronic surveillance programs. But the two countries have no extradition treaty, and Putin dismissed the requests. Putin said he didn't want the Snowden issue to hamper relations with the U.S.

Carney said the U.S. was not told ahead of time of Russia's decision to grant temporary asylum.

Carney did not speculate about what steps, if any, the U.S. might take in response. He noted the complicated and wide-ranging relationship between the two countries and suggested the U.S. is reluctant to let Snowden become the source of further deterioration.

The U.S. and Russia already disagree on many issues, including the civil war in Syria, where Moscow is one of Syrian President Bashar Assad's key supporters. The U.S. supports anti-Assad rebel forces.

There was a strong reaction from some lawmakers Thursday.

"Russia's action today is a disgrace and a deliberate effort to embarrass the United States. It is a slap in the face of all Americans," Republican Sens. John McCain and Lindsey Graham said in a joint statement. "Now is the time to fundamentally rethink our relationship with Putin's Russia."

The senators suggested expanding U.S. sanctions against Russians accused of human rights violations, completing U.S. missile defence programs based in Europe and moving quickly on another round of NATO expansion to include the Republic of Georgia.

A top Democrat, Sen. Chuck Schumer, said Obama should recommend moving the G-20 summit.

Long before Thursday's decision, some lawmakers even suggested a U.S. boycott of the Winter Olympics taking place next year in Sochi, Russia.

Andrew Weiss, a former director of Russian affairs in the Clinton administration, said the Russians had sought an Obama visit so they could portray Putin as an important player on the world stage. But he said it now seems "all but inevitable" that Obama will have to cancel at least part of his trip to Russia.

Jeffery Mankoff, deputy director and fellow with the Russia and Eurasia program at the Center for Strategic and International Studies, said the meeting should go on because of the other important issues on the table.

"All of these things are kind of sitting there in the bilateral relationship and really need a top-level push to get anywhere," Mankoff said.