Snowden left Hong Kong, where he has been in hiding, and flew to Moscow but then apparently did not board a plane bound for Cuba as had been expected. His whereabouts were a mystery. The founder of the WikiLeaks secret-spilling organization, Julian Assange, said he wouldn't go into details about where Snowden was but said he was safe.
Snowden has applied for asylum in Ecuador, Iceland and possibly other countries, Assange said.
Obama, asked if he was confident that Russia would expel Snowden, told reporters: "What we know is that we're following all the appropriate legal channels and working with various other countries to make sure that the rule of law is observed."
Obama's spokesman, Jay Carney, earlier Monday said the U.S. was expecting the Russians "to look at the options available to them to expel Mr. Snowden back to the United States to face justice for the crimes with which he is charged."
"The Chinese have emphasized the importance of building mutual trust," Carney added. "And we think that they have dealt that effort a serious setback. If we cannot count on them to honor their legal extradition obligations, then there is a problem. And that is a point we are making to them very directly."
Snowden has given highly classified documents to The Guardian and The Washington Post newspapers disclosing U.S. surveillance programs that collect vast amounts of phone records and online data in the name of foreign intelligence, often sweeping up information on American citizens. He also told the South China Morning Post that "the NSA does all kinds of things like hack Chinese cellphone companies to steal all of your SMS data."
Snowden still has perhaps more than 200 sensitive documents, Sen. Dianne Feinstein, chairwoman of the Senate Intelligence Committee, said over the weekend.
He had been in hiding in Hong Kong, a former British colony with a degree of autonomy from mainland China. The United States formally sought Snowden's extradition but was rebuffed by Hong Kong officials who said the U.S. request did not fully comply with their laws. The Justice Department rejected that claim, saying its request met all of the requirements of the extradition treaty between the U.S. and Hong Kong.
Said Carney: "We are just not buying that this was a technical decision by a Hong Kong immigration official. This was a deliberate choice by the government to release a fugitive despite a valid arrest warrant, and that decision unquestionably has a negative impact on the U.S.-China relationship."
The dual lines of diplomacy -- harsh with China, hopeful with the Russians -- came just days after Obama met separately with leaders of both countries in an effort to close gaps on some of the major disputes facing them.
Snowden arrived in Moscow on Sunday, but his whereabouts were thrown into question Monday when a plane took off from Moscow for Cuba with an empty seat booked in his name. The U.S. has revoked his passport.
In Washington, U.S. Secretary of State John Kerry said it would be "deeply troubling" if Russia or Hong Kong had adequate notice about Snowden's plans to flee to a country that would grant him asylum and still allowed him leave.
"We don't know, specifically, where he may head, or what his intended destination may be," Kerry said, responding to a question during a news conference in New Delhi where he was discussing bilateral issues between the U.S. and India.
U.S. officials pointed to improved cooperation with the Russians in the aftermath of the Boston Marathon bombing and to assistance the U.S. has given Russia on law enforcement cases.
"We continue to hope that the Russians will do the right thing," Kerry told NBC News. "We think it's very important in terms of our relationship. We think it's very important in terms of rule of law. These are important standards. We have returned seven criminals that they requested for extradition from the United States over the last two years. So we really hope that the right choice will be made here."
"We don't know, specifically, where he may head, or what his intended destination may be," Kerry said during a news conference in New Delhi.
Carney said the U.S. was in touch through diplomatic and law enforcement channels with countries through which Snowden might travel or where he might end up.
"The U.S. is advising these governments that Mr. Snowden is wanted on felony charges and as such should not be allowed to proceed in any further international travel, other than is necessary to return him here to the United States," Carney said.
An Aeroflot representative who wouldn't give her name told The Associated Press that Snowden wasn't on flight SU150 to Havana, which was filled with journalists trying to track him down.
In Moscow, security around the aircraft was heavy prior to boarding and guards tried to prevent the scrum of photographers and cameramen from taking pictures of the plane, heightening the speculation that Snowden might have been secretly escorted on board.
After spending a night in Moscow's Sheremetyevo Airport, Snowden had been expected to fly to Cuba and Venezuela en route to possible asylum in Ecuador.
Some analysts said it was likely that the Russians were questioning Snowden, interested in what he knew about U.S. electronic espionage against Moscow.
"If Russian special services hadn't shown interest in Snowden, they would have been utterly unprofessional," Igor Korotchenko, a former colonel in Russia's top military command turned security analyst, said on state Rossiya 24 television.
The White House's tough response to Hong Kong's decision to let Snowden leave came just two weeks after Obama met with Chinese President Xi Jinping for two days of personal diplomacy in a desert retreat in California.
Carney said that after the U.S. sought Snowden's extradition from Hong Kong, authorities there requested additional information from the U.S.
"The U.S. had been in communication with Hong Kong about these inquiries and we were in the process of responding to the request when we learned that Hong Kong authorities had allowed the fugitive to leave Hong Kong," Carney said.
Ecuador's foreign minister, Ricardo Patino, said his government had received an asylum request, adding Monday that the decision "has to do with freedom of expression and with the security of citizens around the world."
Ecuador has rejected some previous U.S. efforts at cooperation and has been helping Assange avoid prosecution by allowing him to stay at its embassy in London.
But Assange's comments that Snowden had applied in multiple places opened other possibilities of where he might try to go.
WikiLeaks has said it is providing legal help to Snowden at his request and that he was being escorted by diplomats and legal advisers from the group.
Icelandic officials have confirmed receiving an informal request for asylum conveyed by WikiLeaks, which has strong links to the tiny North Atlantic nation. But authorities there have insisted that Snowden must be on Icelandic soil before making a formal request.
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