The U.S. hunt for National Security Agency leaker Edward Snowden came to a boil Monday as the White House ripped into Hong Kong and China and issued warnings to Russia and Ecuador, where Mr. Snowden has sought asylum, sharply dialing up global pressure for his return to face espionage charges.

The case of Mr. Snowden, under federal indictment for stealing and leaking classified documents, has become a test of Washington's ability to influence unsympathetic governments. Having failed after weeks of work through international legal channels, the U.S. turned to an aggressive diplomatic strategy.

President Barack Obama, Secretary of State John Kerry and officials at the White House and Justice Department took turns asking for Mr. Snowden's return to the U.S. amid warnings that relations would be strained.

China was singled out for particular criticism after Mr. Snowden unexpectedly left Hong Kong on Sunday for Moscow in defiance of a U.S. demand for his extradition.

U.S. officials implied that Beijing scuttled what had been a steadily advancing process of establishing a case that would lead to extradition proceedings.

"The Chinese have emphasized the importance of building mutual trust," said White House spokesman Jay Carney. "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."

U.S. officials said talks were under way with Moscow, and that they thought the Russians were taking the matter "seriously."

While they warned of unspecified "repercussions," administration officials on Monday stopped short of identifying actions the U.S. might take against governments that refused to comply.

Officials in Ecuador said Mr. Snowden has applied for asylum, and they are considering the request. If he ends up there, the tiny Latin American country—which last year granted asylum to WikiLeaks founder Julian Assange, who is holed up in Ecuador's London embassy and working to aid Mr. Snowden—could feel the most direct brunt of U.S. displeasure.

The U.S. is Ecuador's most important trading partner, accounting for $10.7 billion, or 43%, of its total exports. But a key U.S. trade preference measure expires next month, and U.S. lawmakers could retaliate by refusing to renew it, administration officials said.

With U.S.-Russian talks under way, American officials declined to specify possible U.S. action against Moscow. International experts said the U.S. could pressure Russia before the World Trade Organization, where it has been a member for about a year, over trade policies. U.S. officials also could try to press Russia over sanctions related to Iran or Syria.

The U.S. also could act in areas it knows would irritate China and Russia: moving ahead with a global missile defense expansion, or taking new steps to enlarge international groups such as the North Atlantic Treaty Organization or the Association of Southeast Asian Nations.

U.S. officials acknowledge they have limited leverage with Moscow. In private talks, the U.S. has held out the possibility of unspecified greater cooperation with Russia in the future if it helps Washington in the Snowden case, officials said.

Most likely, however, the U.S. will continue a drumbeat of criticism of these nations for failing to honor commitments to cooperate with other nations. Harsher steps are seen as a threat to other U.S. priorities for which it needs Russian and Chinese help: to contain the Syrian civil war, North Korea's provocations and Iran's nuclear program.

Mr. Snowden's case has Cold War overtones and brought old rivals face to face. Moscow hasn't made clear its role in Mr. Snowden's global odyssey. A spokesman for Russian President Vladimir Putin said Monday that questions about Mr. Snowden were a matter for Russia's Ministry of Foreign Affairs, which didn't respond to numerous requests for comment.

Russian authorities were mum on Mr. Snowden's whereabouts. Russia's state-controlled Channel 1 carried an ironic report about "Finding Mr. Snowden," highlighting journalists' failed efforts to locate the fugitive.

Mr. Assange said during a news conference from London that Mr. Snowden was being aided by the WikiLeaks organization and was destined for Ecuador. Reports in Russian media said he was awaiting a flight to Cuba, where he would seek transit to Quito, Ecuador. There are no direct flights from Moscow to Quito. But Mr. Snowden wasn't on a plane bound for Havana for which Russian news outlets said he had booked a ticket.

Mr. Carney said U.S. officials were in contact with governments of countries Mr. Snowden reportedly has been considering as a destination.

President Obama, asked whether he had spoken with Mr. Putin, said: "What we know is that we're following all the appropriate legal channels and working with various other countries to make sure that rule of law is observed."

U.S. officials defended the Justice Department's handling of negotiations with Hong Kong. Justice Department officials formally asked Hong Kong on June 15 for Mr. Snowden's arrest, a day after they filed a three-count criminal complaint under seal in federal court in Alexandria, Va.

A U.S. official briefed on the discussions said Justice Department lawyers consulted with Hong Kong authorities in tailoring the three charges to meet the guidelines of a treaty between the two countries: theft of government property; unauthorized communication of national defense information; and willful communication of classified communications intelligence.

On June 19, Attorney General Eric Holder contacted his counterpart in Hong Kong, "stressing the importance of the matter and urging Hong Kong to honor our request for Snowden's arrest," said Mr. Carney.

Last Friday, Hong Kong asked for more information, U.S. officials said. "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," Mr. Carney said.

Neither Mr. Carney nor other officials would say what they believed happened. But they rejected as an explanation for Hong Kong's action any technical problem with their request.

"We are just not buying that this was a technical decision by a Hong Kong immigration official," said Mr. Carney about Mr. Snowden's flight from Hong Kong on Sunday. "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."

Two of the three U.S. charges against Mr. Snowden are espionage-related. As such, they pose problems for any U.S. attempt to seek a "red notice" from Interpol, the international police agency, which could have sought an arrest in all 190 member countries. Interpol's rules don't allow arrest warrants for political matters, under which espionage charges would fall.

The U.S. updated Interpol's databases to show that Mr. Snowden's passport had been suspended, one U.S. official said. Another U.S. official said the U.S. never sought a "red notice" or felt it needed one in part because American officials were in negotiations with Hong Kong and believed that involving the international police agency wouldn't be necessary.

A published account Monday said Mr. Snowden admitted he sought out his position at contractor Booz Allen Hamilton to gather evidence about NSA surveillance programs.

"My position with Booz Allen Hamilton granted me access to lists of machines all over the world the NSA hacked," he said in a June 12 interview, the South China Morning Post reported. "That is why I accepted that position about three months ago."

Mr. Snowden has said he leaked documents from the agency to shed light on a program to collect metadata from U.S. telephone companies—information about phone calls, though not the content of the calls—and another operation aimed at monitoring online activities of non-U.S. residents.

Ecuador's foreign minister, Ricardo Patino, at a news conference in Hanoi, Vietnam, described Mr. Snowden's request for asylum as one based on "freedom of expression and with the security of citizens around the world."

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