The White House issued a sharp warning Monday that Hong Kong's decision to allow fugitive leaker Edward Snowden to leave had harmed efforts to build trust in US-China relations.

In unusually direct criticism of Beijing, White House spokesman Jay Carney said the White House did not accept explanations that the decision was simply a determination handed down by local Hong Kong authorities.

"With regards to ... the Chinese government, we are just not buying that this was a technical decision by a Hong Kong immigration official," he said.

"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.

"The Chinese have emphasized the importance of building mutual trust.

"We think that they have dealt that effort a serious setback. If we cannot count on them to honor their legal extradition obligations, then there is a problem. And that is a point we are making to them very directly."

Earlier this month, President Barack Obama and new Chinese President Xi Jinping made an effort to improve trust and cooperation between Beijing and Washington at a summit in California.

But the Snowden affair erupted just days later and could now frustrate those efforts.

Carney also told reporters the White House believes Russia should accept America's request for Snowden to be expelled back to the United States.

"We do expect the Russian government to look at all the options available to him to expel Mr Snowden back to the United States," he said.

Carney also noted intensified cooperation on law enforcement with Russia after the Boston bombings and had returned "numerous high-level criminals back to Russia at the request of the Russian government."

He refused to speculate on the implications of any failure by Russia to hand over Snowden, who was last believed to be in a transit area of Moscow airport.

He also said that Washington had been in touch with countries through which Snowden might transit, noting that he was a fugitive from felony charges in the United States.

Snowden has asked for asylum in Ecuador, and Carney hinted that Washington had already contacted the Ecuadoran government over Snowden. Ecuador had earlier confirmed that Washington had been in touch.

AFP