The United States is disappointed by Hong Kong's "troubling" failure to arrest fugitive intelligence leaker Edward Snowden before he fled the territory, an official said on Sunday.
A Department of Justice spokesperson insisted US officials had fulfilled all the requirements of Washington's extradition treaty with the autonomous Chinese region and were "disappointed" by the decision to let him go.
Snowden, a 30-year-old former intelligence contractor, is wanted by the United States on espionage charges, after he quit his job with the National Security Agency and fled to Hong Kong with a cache of secret documents.
On Sunday, Snowden left Hong Kong and fled for Moscow, despite Washington having requested his arrest and extradition. Hong Kong officials said the documentation supporting the extradition request had been incomplete.
But the US Department of Justice denied there was anything missing.
"The US is disappointed and disagrees with the determination by Hong Kong authorities not to honor the US request for the arrest of the fugitive," the spokesperson said in a statement.
"The request for the fugitive's arrest for purposes of his extradition complied with all of the requirements of the US-Hong Kong Surrender Agreement," the statement said.
"At no point, in all of our discussions through Friday, did the authorities in Hong Kong raise any issues regarding the sufficiency of the US's provisional arrest request," it said.
"In light of this, we find their decision to be particularly troubling."
The statement said senior US officials had been in touch with their Hong Kong counterparts since June 10, when they learned Snowden was in Hong Kong and leaking details of secret surveillance programs to the media.
On Wednesday, US Attorney General Eric Holder spoke to Hong Kong Secretary for Justice Rimsky Yuen and urged Hong Kong to honor the request for Snowden's arrest.
The Hong Kong government had said that, as it "has yet to have sufficient information to process the request for provisional warrant of arrest, there is no legal basis to restrict Mr Snowden from leaving Hong Kong."