On a visit to India, US Secretary of State John Kerry said it was "deeply troubling" if requests for the former spy's extradition had been ignored -- and warned of consequences for Sino-US relations.
Despite its fury, Washington has been on the defensive for weeks as Snowden stepped up a drip-feed of leaks from his Hong Kong bolthole, including allegations of extensive US snooping on targets in the city and mainland China.
The Hong Kong government insisted that its decision to let the 30-year-old Snowden fly out yesterday was governed strictly by the law, after a provisional US arrest warrant purportedly failed to meet its judicial requirements.
Breaking his long silence on the affair, Hong Kong leader Leung Chun-ying today said "the people of Hong Kong expect Hong Kong to uphold its own laws".
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The White House said it was "just not buying" explanations that the decision was simply a determination handed down by local Hong Kong authorities.
"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 US-China relationship," spokesman Jay Carney said.
For many observers, such a high-profile case -- carrying the potential to destabilise Sino-US ties for years if Snowden had fought a lengthy legal battle in Hong Kong -- must have provoked intense interest among the territory's overseers.
Lau argued that Hong Kong's government was a pawn, with Beijing guiding the pieces.
"Hong Kong is just part of a chess game. It was the same when it was part of Britain," he told AFP.