The former National Security Agency contractor and CIA technician fled Hong Kong and arrived at the Moscow airport, where he planned to spend the night before boarding an Aeroflot flight to Cuba. Ecuador's Foreign Minister Ricardo Patino said his government received an asylum request from Snowden, and the anti-secrecy group WikiLeaks said it would help him.
"He goes to the very countries that have, at best, very tense relationships with the United States," said Rep. Ileana Ros-Lehtinen, R-Fla., adding that she feared Snowden would trade more U.S. secrets for asylum. "This is not going to play out well for the national security interests of the United States."
The move left the U.S. with limited options as Snowden's itinerary took him on a tour of what many see as anti-American capitals. Ecuador in particular has rejected the United States' previous efforts at co-operation, and has been helping WikiLeaks founder, Julian Assange, avoid prosecution by allowing him to stay at its embassy in London.
Snowden gave The Guardian and The Washington Post documents disclosing U.S. surveillance programs that collect vast amounts of phone records and online data in the name of foreign intelligence, but often sweep up information on American citizens. Officials have the ability to collect phone and Internet information broadly but need a warrant to examine specific cases where they believe terrorism is involved.
Snowden had been in hiding for several weeks in Hong Kong, a former British colony with a high degree of autonomy from mainland China. The United States formally sought Snowden's extradition from Hong Kong but was rebuffed; Hong Kong officials 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.
During conversations last week, including a phone call Wednesday between Attorney General Eric Holder and Hong Kong Secretary for Justice Rimsky Yuen, Hong Kong officials never raised any issues regarding sufficiency of the U.S. request, a Justice spokesperson said.
A State Department official said the United States was in touch through diplomatic and law enforcement channels with countries that Snowden could travel through or to, reminding them that Snowden is wanted on criminal charges and reiterating Washington's position that Snowden should only be permitted to travel back to the U.S.
Those officials spoke on condition of anonymity because they were not authorized to publicly discuss the case.
The Justice Department said it would "pursue relevant law enforcement co-operation with other countries where Mr. Snowden may be attempting to travel."
Russia's state ITAR-Tass news agency and Interfax cited an unnamed Aeroflot airline official as saying Snowden was on the plane that landed Sunday afternoon in Moscow.
Upon his arrival, Snowden did not leave Moscow's Sheremetyevo Airport. One explanation could be that he wasn't allowed; a U.S. official said Snowden's passport had been revoked, and special permission from Russian authorities would have been needed.
Caitlin Hayden, a spokeswoman for the White House's National Security Council, said, "Given our intensified co-operation after the Boston marathon bombings and our history of working with Russia on law enforcement matters — including returning numerous high-level criminals back to Russia at the request of the Russian government — we expect the Russian government to look at all options available to expel Mr. Snowden back to the U.S. to face justice for the crimes with which he is charged."
The Russian media report said Snowden intended to fly to Cuba on Monday and then on to Caracas, Venezuela.
U.S. lawmakers scoffed. "The freedom trail is not exactly China-Russia-Cuba-Venezuela, so I hope we'll chase him to the ends of the earth, bring him to justice and let the Russians know there'll be consequences if they harbour this guy," said Sen. Lindsey Graham, R-S.C.
With each suspected flight, efforts to secure Snowden's return to the United States appeared more complicated if not impossible. The United States does not have an extradition treaty with Russia, but does with Cuba, Venezuela and Ecuador. Even with an extradition agreement though, any country could give Snowden a political exemption.
The likelihood that any of these countries would stop Snowden from travelling on to Ecuador seemed remote. While diplomatic tensions have thawed in recent years, Cuba and the United States are hardly allies after a half century of distrust.
Venezuela, too, could prove difficult. Former President Hugo Chavez was a sworn enemy of the United States and his successor, Nicolas Maduro, earlier this year called Obama "grand chief of devils." The two countries do not exchange ambassadors.
U.S. pressure on Caracas also might be problematic given its energy exports. The U.S. Energy Information Agency reports Venezuela sent the United States 900,000 barrels of crude oil each day in 2012, making it the fourth-largest foreign source of U.S. oil.
"I think 10 per cent of Snowden's issues are now legal, and 90 per cent political," said Douglas McNabb, an expert in international extradition and a senior principal at international criminal defence firm McNabb Associates.
Assange's lawyer, Michael Ratner, said Snowden's options aren't numerous.
"You have to have a country that's going to stand up to the United States," Ratner said. "You're not talking about a huge range of countries here."
That is perhaps why Snowden first stopped in Russia, a nation with complicated relations with Washington.
Russian President Vladimir Putin is "aiding and abetting Snowden's escape," said Sen. Chuck Schumer, D-N.Y.
"Allies are supposed to treat each other in decent ways, and Putin always seems almost eager to put a finger in the eye of the United States," Schumer said. "That's not how allies should treat one another, and I think it will have serious consequences for the United States-Russia relationship."
It also wasn't clear Snowden was finished with disclosing highly classified information.
"I am very worried about what else he has," said Rep. Loretta Sanchez, a California Democrat who sits on the House Homeland Security Committee.
Sen. Dianne Feinstein, the chairwoman of the Senate Intelligence Committee, said she had been told Snowden had perhaps more than 200 sensitive documents.
Ros-Lehtinen spoke with CNN. Graham spoke to "Fox News Sunday." Schumer was on CNN's "State of the Union." Sanchez appeared on NBC's "Meet the Press." Feinstein was on CBS' "Face the Nation."
Associated Press White House Correspondent Julie Pace and Associated Press writers Matthew V. Lee and Frederic J. Frommer in Washington, Lynn Berry in Moscow, Kevin Chan in Hong Kong and Sylvia Hui in London contributed to this report.
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