China interceded to allow Edward Snowden's dramatic flight from Hong Kong, calculating that infuriating the United States for now was necessary to prevent longer-term corrosion to their relationship, analysts and media said Monday.

On a visit to New Delhi, 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.

Beijing formally protested after the latest revelations came out at the weekend -- just as Snowden was deserting Hong Kong. State media called Washington a "villain" for its alleged hacking, flagging up the irony that the United States has long portrayed itself as a victim of Chinese cyber-espionage.

The Hong Kong government insisted that its decision to let the 30-year-old Snowden fly out on Sunday 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 on Monday said "the people of Hong Kong expect Hong Kong to uphold its own laws".

In Beijing, the foreign ministry said the central government "always respects" Hong Kong's relative autonomy but sidestepped the allegations that it orchestrated Snowden's departure.

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.

Hong Kong political analyst Johnny Lau said he believed that Chinese representatives "must have drained him in depth and exhausted him (for intelligence) before letting him go".

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.

Albert Ho, one of Hong Kong's most respected pro-democracy lawmakers, revealed that he had been hired as Snowden's lawyer and that he had relayed a message from a mystery intermediary several days ago.

The intermediary did not specify whether he represented the government in Beijing or Hong Kong, but Ho said: "I have reasons to believe that... those who wanted him to leave represented Beijing authorities.

"Bejing would not step forward to the front stage because it (would) affect Sino-US relations," he told reporters.

"So, it would operate behind the scenes to make Snowden go. The Hong Kong government may not have had any role other than not stopping him at the airport."

After arriving in Hong Kong on May 20, armed with laptops containing a wealth of information on National Security Agency (NSA) eavesdropping of private Internet users and cellphones around the world, Snowden explained his choice of destination in a newspaper interview.

"My intention is to ask the courts and the people of Hong Kong to decide my fate. I have been given no reason to doubt your system," he told the South China Morning Post.

But something changed over the weekend, after the United States issued its arrest warrant with a view to instituting formal extradition proceedings.

The former NSA contractor and CIA agent fetched up in Moscow where he was last believed to be in a transit area of the airport, and has asked Ecuador to grant him asylum.

Aghast lawmakers in Washington expressed strong suspicion of Chinese as well as Russian meddling.

"I had actually thought that China would see this as an opportunity to improve relations and extradite him to the United States," Senate Intelligence Committee chairwoman Dianne Feinstein said on CBS television.

"China clearly had a role in this, in my view."

Whatever the answer, newspapers in China and Hong Kong said Beijing had no interest in allowing Snowden's fate to fester as the new government of President Xi Jinping looks to reboot its overarching relationship with the United States after a troubled period.

The South China Morning Post declared in an editorial: "There could be no better outcome for our city and China."

Shen Dingli, an international relations professor at Fudan University in Shanghai, agreed that Beijing probably took the final decision on the Snowden case.

"For such a vital national security interest, how can Hong Kong decide by itself? If we want to have good US-China relations, it benefits China" to have let Snowden leave, he said.

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