WASHINGTON — The former National Security Agency contractor who disclosed a highly classified surveillance program has had his U.S. passport revoked, an official said Sunday.

Edward Snowden's passport was annulled before he left Hong Kong for Russia and while that could complicate his travel plans, the lack of a passport alone could not thwart his plans, the U.S. official said. If a senior official in another country or with an airline orders it, a country could overlook the withdrawn passport, the official said.

The U.S. official would only discuss the passport on the condition of anonymity because the official was not authorized to discuss the matter.

Snowden's allies said he was heading toward Ecuador, where the foreign minister said the government had received a request for asylum.

State Department spokeswoman Jen Psaki refused to comment on Snowden's passport specifically but said individuals facing arrest warrants could have their passport withdrawn.

"Such a revocation does not affect citizenship status. Persons wanted on felony charges, such as Mr. Snowden, should not be allowed to proceed in any further international travel other than is necessary to return him to the United States," Psaki said in a statement.

The State Department said the United States was in touch, through diplomatic and law enforcement channels, with countries that Snowden might travel through or to.

Snowden, a CIA technician and former NSA contractor, helped The Guardian and The Washington Post to disclose surveillance programs that collects vast amounts of online data and email, sometimes sweeping up information on ordinary 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.

Since news organizations began publishing reports based on Snowden's disclosures, he had been in hiding 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.

Snowden was said to have landed in Moscow on Sunday but was not seen leaving the airport.

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