The United States revoked leaker Edward Snowden's passport Sunday and said he should be barred from travel as he fled to Moscow en route to Ecuador, potentially setting off a diplomatic crisis.

The fugitive IT specialist, who revealed secret details of vast US telephone and Internet surveillance programs to the media, left Hong Kong despite a US extradition request and was at a hotel in a Moscow airport.

US State Department spokeswoman Jen Psaki, traveling with Secretary of State John Kerry in India, confirmed that the United States revoked Snowden's passport due to "felony arrest warrants" against him.

A State Department official said the United States has been in contact with "countries in the Western Hemisphere through which Snowden might transit or that could serve as final destinations."

"The US 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" unless he is being returned to the United States.

"The chase is on," California Senator Dianne Feinstein said as the Snowden affair grew vastly more complicated for President Barack Obama, potentially testing US relations with Russia and other nations.

Feinstein, chair of the Senate Intelligence Committee, said she had learned Snowden may have more material to leak -- "over 200 separate items."

"I think we need to know exactly what he has. He could have a lot, lot more. It may really put people in jeopardy. I don't know," she told CBS news.

WikiLeaks said unidentified diplomats and WikiLeaks legal advisers are escorting Snowden, 30, a former IT contractor at the National Security Agency, in his bid to secure political asylum in an undisclosed country.

US authorities filed espionage charges against Snowden last week and asked Hong Kong to detain him on a provisional arrest warrant.

But Snowden boarded an Aeroflot flight for Moscow on Sunday, and Ecuador said he had requested asylum in the South American country, which is governed by President Rafael Correa, a leftist critic of the United States.

Ecuador has been sheltering WikiLeaks founder Julian Assange at its London embassy for the past year.

Snowden left his home in Hawaii on May 20 and flew to Hong Kong, a semi-autonomous Chinese territory, from where he proceeded to leak details of the secret US intelligence programs to the Guardian and the Washington Post.

The leaks have embarrassed Obama's administration, which was forced to defend US intelligence agencies' practice of gathering US phone call logs and vast quantities of Internet data from private users around the world.

New York Senator Chuck Schumer told CNN it was "very disappointing" that Hong Kong had allowed Snowden to leave, adding that it "remains to be seen how much influence Beijing had on Hong Kong."

He also accused Russian President Vladimir Putin of "aiding and abetting Snowden's escape."

"Putin always seems almost eager to put a finger in the eye of the United States," he said, adding that Moscow's allowing Snowden to travel onward would have "serious consequences" for bilateral relations.

NSA chief General Keith Alexander, meanwhile, said the leaks had forced a tightening of security on IT system operators like Snowden, who "betrayed the trust and confidence we had in him" and "stole some of our secrets."

"We are now putting in place actions that would give us the ability to track our system administrators, what they're doing, what they're taking," he told ABC News.

"We've changed the passwords," Alexander said. "But at the end of the day we have to trust that our people are going to do the right thing."

The NSA chief also repeated assertions that the spy programs were needed to prevent terror attacks and had helped foil some 50 plots around the world.