MOSCOW - Edward Snowden, the fugitive former National Security Agency contractor wanted by the United States for leaking classified documents about global U.S. surveillance, fled his Hong Kong hide-out for Moscow on Sunday aboard a Russian jetliner, in what appeared to be the first step in an odyssey to seek political asylum in another country, possibly Ecuador or Venezuela.

U.S. authorities scrambled Sunday to figure out how to catch Snowden, frustrating President Barack Obama’s administration and threatening to strain relations on three continents.

Snowden boarded an Aeroflot jetliner in Hong Kong that reached Moscow on Sunday afternoon. The Russian Foreign Ministry said Snowden was in a Moscow airport transit area, apparently awaiting a connection to another country.

U.S. officials were seeking Snowden’s extradition from Hong Kong when they learned of his departure, according to a Justice Department official with knowledge of the matter.

“The chase is on,” Senate Intelligence Committee Chairman Dianne Feinstein said in an interview on CBS’ Face the Nation.

Diplomats and law enforcement officials from the United States warned countries in Latin America not to harbor Snowden or allow him to pass through to other destinations after he fled Hong Kong for Moscow, possibly en route to Ecuador or another nation where he could seek asylum.

Snowden managed to elude capture just as U.S. officials were asking Hong Kong authorities to detain and send him to the United States on charges that he illegally disclosed classified documents about global U.S. surveillance programs. He was aided in his escape by WikiLeaks, the anti-secrecy organization, whose founder said he helped arrange special refugee travel documents from Ecuador.

The foreign minister of Ecuador confirmed receiving an asylum request from Snowden. As of early this morning in Russia, Snowden was believed to be staying the night inside the transit zone of a Moscow airport where he was visited by an Ecuadorean diplomat. It was not clear whether he would be allowed to travel further or, if he were, whether Ecuador would indeed be his final destination.

Russian news services reported that Snowden would take a flight to Cuba today, prompting a late rush for tickets from the horde of journalists gathered at the airport. But others dismissed it as a ruse to put the news media and others off Snowden’s trail.

The turn of events opened a startling new chapter in a case that had already captivated many in the United States andaround the world. Snowden’s transcontinental escape could be seen as an embarrassment for the Obama administration and raised questions about its tactics in the case, such as its failure to immediately revoke Snowden’s passport.

It also further complicated Washington’s ties with Russia and China, where at least some officials take delight in tweaking what they call American double standards.

Julian Assange, the founder of WikiLeaks, said in an interview from his own refuge in the Ecuadorean Embassy in London that he had raised Snowden’s case with Ecuador’s government and that his group had helped arrange the travel documents. Baltasar Garzon, the renowned Spanish jurist who advises WikiLeaks, said in a statement that “what is being done to Mr. Snowden and to Mr. Julian Assange - for making or facilitating disclosures in the public interest - is an assault against the people.”

Obama administration officials privately expressed frustration that Hong Kong allowed Snowden to leave for Moscow on Sunday despite the American request for his detention. But they did not revoke Snowden’s passport until Saturday and did not ask Interpol to issue a “red notice” seeking his arrest.

An administration official, speaking on condition of anonymity, said no red notice was requested because they are “most valuable when the whereabouts of a fugitive are unknown.” Snowden was known to be in Hong Kong, so his provisional arrest was sought under an existing American agreement with Hong Kong.

On Sunday, the Hong Kong authorities said that the American arrest request “did not fully comply with the legal requirements under Hong Kong law,” and therefore they could not legally stop Snowden from leaving. The Justice Department rejected this explanation and provided a timeline of interactions suggesting that the Hong Kong authorities first requested “additional information” Friday.

“At no point, in all of our discussions through Friday,did the authorities in Hong Kong raise any issues regarding the sufficiency of the U.S.’ provisional arrest request,” a department official said. “In light of this, we find their decision to be particularly troubling.”

By the end of the day U.S. officials, unsure whether Snowden was actually heading to Ecuador, or possibly Cuba or Venezuela, as also was reported, were sending messages to an array of possible destinations.

“The U.S. is advising these governments that 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 to the United States,” a State Department official said in a statement.

Obama, who has drawn criticism since the disclosure of domestic telephone data and foreign Internet communications surveillance programs, remained silent on the latest developments Sunday. Aides said only that he was being updated by national security officials and that he had not made any telephone calls personally to foreign leaders seeking cooperation.

While officials said Snowden’s passport was revoked Saturday, it was not clear whether the Hong Kong authorities knew by the time he boarded the plane, nor was it clear whether revoking it earlier would have made a difference given the Ecuadorean travel document that Assange said he helped arrange. When Snowden landed in Moscow, he was informed of his passport revocation.

Assange said he did not know whether Snowden might be able to travel beyond Moscow using the Ecuadorean document. “Different airlines have different rules so it’s a technical matter whether they will accept the document,” he said.

Assange sought refuge in the Ecuadorean Embassy in London a year ago to avoid being sent to Sweden for questioning in a sexual-offense investigation, but British authorities have not permitted him to leave the country without risking arrest. Snowden could end up in a similar predicament, accepted by Ecuador or another country but unable to get there.

Snowden’s presence on Russian territory dealt a fresh blow to a relationship that has deteriorated sharply over the past year over issues such as Syria and human rights. Yet Russian leaders seemed to be making efforts to keep his visit relatively quiet, not parading Snowden before cameras or trumpeting his arrival.

New York Sen. Charles Schumer, the third-ranked Democrat in the Senate, said he thought Russian President Vladimir Putin may have known and approved of Snowden’s flight.

“Putin always seems almost eager to put a finger in the eye of the United States,” Schumer said on CNN’s State of the Union program. “That’s not how allies should treat one another, and I think it will have serious consequences for the United States-Russia relationship.”

Schumer also pointed to China, calling Hong Kong’s decision to allow Snowden to leave “very disappointing” and saying that he had “a feeling the hand of Beijing was involved here.”

“We have nothing to do with this story,” said Dmitri Peskov, a spokesman for Putin. “I am not in charge of tickets. I don’t approve or disapprove plane tickets. We’re not the proper people to address this question to.”

But Dmitri V. Trenin, director of the Carnegie Moscow Center, said Snowden could remain in Russia, a country that is increasingly positioning itself as a protector of people like Assange, whom Western governments wish to prosecute.

“Russia is turning into a haven - virtually, intellectually and physically - for those who have an ax to grind with the West, who are whistle-blowers or have problems with Western authorities,” he said. “It’s the only country in the world that at this point can afford it, or thinks it can afford it.”

Ecuador, like Cuba and Venezuela, has expressed antipathy toward what it considers arrogant U.S. policies in Latin America and demonstrated with its decision to shelter Assange that it was willing to defy Washington. Ricardo Patino Aroca, the country’s foreign minister, said in a Twitter message that an asylum request from Snowden had been received, and he later scheduled a news conference for today.

How long Snowden can evade arrest remained to be seen. In an interview with The Guardian earlier this month, he expressed pessimism.

“You can’t come up against the world’s most powerful intelligence agencies and not accept the risk,” he said. “If they want to get you, over time they will.”

In other developments, Glenn Greenwald, the Guardian writer who first reported Snowden’s disclosure of U.S. government surveillance programs, appeared on NBC’s Meet the Press on Sunday.

During his interview with NBC’s David Gregory, Greenwald declined to discuss where Snowden was headed. That refusal seemed to prompt Gregory to ask: “To the extent that you have aided and abetted Snowden, even in his current movements, why shouldn’t you, Mr. Greenwald, be charged with a crime?”

Greenwald said it’s “pretty extraordinary that anybody who would call themselves a journalist would publicly muse about whether or not other journalists should be charged with felonies.”

Greenwald said Gregory was embracing the Obama administration’s attempt to “criminalize investigative journalism,” citing an FBI agent’s characterization of Fox News journalist James Rosen as a probable co-conspirator of a State Department contractor who was suspected of leaking classified information to Rosen. Rosen was not charged.

“If you want to embrace that theory, it means that every investigative journalist in the United States who works with their sources, who receives classified information is a criminal, and it’s precisely those theories and precisely that climate that has become so menacing in the United States,” said Greenwald, a former constitutional and civilrights lawyer who has written three books contending that the government has violated personal rights in the name of protecting national security.

Information for this article was contributed by Ellen Barry, Andrew Roth, Rick Gladstone, Scott Shane, Michael R. Gordon, Charlie Savage, Steven Lee Myers and Keith Bradsher of The New York Times; by Phil Mattingly and Lorraine Woellert of Bloomberg News; and by Frederic J. Frommer and staff members of The Associated Press.

Front Section, Pages 1 on 06/24/2013