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Fugitive US intelligence leaker Edward Snowden has requested a meeting with leading Russian rights activists and lawyers at the airport in Moscow, campaigners said, as the United States took aim at China for not handing him over.

The Interfax news agency reported those invited to the airport, where Snowden has been stuck in transit for the last three weeks, included representatives of Amnesty International, Human Rights Watch and Transparency International as well as several prominent lawyers working in Moscow.

Prominent Moscow lawyer Genrikh Padva confirmed to AFP that he had received an invitation for a meeting at the airport Friday afternoon.

"We received such a letter from him and the Moscow airport telephoned as well," he said, adding he did not believe he would have time to attend.

Sergei Nikitin of the Moscow branch of Amnesty International said the group received an email inviting his group and said "we are planning to go." Elena Panfilova of Transparency International said the "somewhat unexpected" invitation was being discussed.

Panfilova said the email had come from an apparently secure email address in Snowden's name.

A source at Sheremetyevo airport told Interfax earlier that the former intelligence employee wanted to make an announcement to the activists and lawyers.

"He wants to express his opinion about the manic campaign of the persecution against him unleashed by the United States which means that passengers on flights to Latin America are in danger," the source told the agency.

The source did not give further details but leftist Latin American states such as Venezuela and Ecuador are seen as the most likely destination for Snowden to seek asylum.

Earlier Washington told China it was upset it did not hand over Snowden after he fled to Hong Kong, saying that the decision had undermined relations.

President Barack Obama, meeting senior Chinese officials who were in Washington for annual wide-ranging talks, "expressed his disappointment and concern" over the Snowden case, the White House said in a statement.

Deputy Secretary of State William Burns, one of the main US officials in the talks, said Obama and Chinese President Xi Jinping agreed at their summit last month at the California resort of Sunnylands to cooperate over problems.

"That is why we were very disappointed with how the authorities in Beijing and Hong Kong handled the Snowden case, which undermined our effort to build the trust needed to manage difficult issues," Burns said.

"We have made clear that China's handling of this case was not consistent with the spirit of Sunnylands or with the type of relationship -- the new model -- that we both seek to build," Burns said at a joint press event.

The Interfax news agency reported Friday that Snowden has requested a meeting with leading rights activists and lawyers at the airport in Moscow where he has been stuck in transit for the last three weeks.

The agency said those invited included representatives of Amnesty International and Human Rights Watch. Prominent Moscow lawyer Genrikh Padva confirmed to AFP that he had received such an invitation for a meeting at the airport Friday afternoon.

Snowden, a former government contractor, fled the United States for Hong Kong after revealing details of pervasive US intelligence surveillance on the Internet. The United States sought his extradition to face charges.

But Snowden was allowed to leave Hong Kong, a territory of China that enjoys a large amount of autonomy, for Russia.

Since arriving in Russia on June 23, Snowden has been stuck in the transit zone of Moscow's Sheremetyevo Airport as he seeks a way to get to a country that will offer him asylum.

State Councilor Yang Jiechi, speaking next to Burns, defended decisions on Snowden, whose allegations of US snooping in Chinese Internet networks caused a stir in Beijing.

"The central government of China has always respected the Hong Kong Special Administrative Region government's handling of cases in accordance with the law," he said.

Hong Kong "handled the Snowden case in accordance with the law and its approach is beyond reproach", said Yang, a central figure in Chinese foreign policy.

"The Americans are just trying to save face," said Hong Kong pro-democracy lawmaker Claudia Mo, dismissing the rebuke from Washington as "diplomatic talk".

"The Chinese didn't exactly invite Snowden to come to Hong Kong," Mo told AFP.

Hong Kong executive council member Bernard Chan was also critical of Washington, saying "Hong Kong and China were not the ones at fault".

"It was the US, not Hong Kong, that decided to operate a global electronic spying operation, which even some Americans now believe is out of control," Chan wrote in the South China Morning Post.

"It was the US, not Hong Kong, that decided directly or via outsourcing to use the services of a young man who turned out to be disloyal."

Earlier Thursday, Russia's Interfax news agency said the US had stopped pressing Russia to extradite Snowden, quoting a source close to the situation.

"There has not been any request either through official or unofficial channels for several days now," the source told the agency.

Snowden has applied for asylum in 27 countries.

Although many of them have already turned down his request, Venezuelan President Nicolas Maduro offered "humanitarian asylum" to Snowden last week.