Bolivia has said President Evo Morales' plane was forced to land in Austria after France and Portugal refused air permits, apparently because they suspected it was carrying Edward Snowden, the former US spy agency contractor wanted by Washington on espionage charges.

Bolivian Foreign Minister David Choquehuanca on Tuesday furiously accused France and Portugal of putting Morales' life at risk and insisted that Snowden was not on Morales' plane.

Choquehuanca told reporters that Portugal and France had abruptly cancelled the air permits, forcing the unscheduled Vienna stopover as Morales was returning on a Bolivian government aircraft from Russia.

"They say it was due to technical issues, but after getting explanations from some authorities we found that there appeared to be some unfounded suspicions that Mr Snowden was on the plane ... We don't know who invented this lie," he said.

"We want to express our displeasure because this has put the president's life at risk."

While attending an energy conference in Russia this week, Morales said he would consider granting asylum to Snowden if requested.

Bolivian Defence Minister Ruben Saavedra said the US State Department may have been behind the decisions to not allow Morales' plane to land in Portugal or fly over French air space.

"We have the suspicion that they (the two European governments) were used by a foreign power, in this case the United States, as a way of intimidating the Bolivian state and President Evo Morales," he said.

Dwindling asylum options

Countries in Latin America, Asia and Europe have spurned asylum requests by Snowden, despite a call by Venezuela for the world to protect the former US spy agency contractor.

Snowden, who revealed the secret US electronic surveillance programme, PRISM, has applied for political asylum in more than a dozen countries in his search for safety from prosecution in the United States.

The 30-year-old American is in legal limbo in the transit area of Moscow's Sheremetyevo airport, unable to fly out because he has no legal travel documents and also has no Russian visa to leave the airport.

On Monday, the whistleblower broke a nine-day silence since arriving in Moscow from Hong Kong, challenging Washington by saying he was free to publish more about its programmes and that he was being illegally persecuted.

That ruled out a prolonged stay in Russia, where a spokesman for President Vladimir Putin said Snowden had withdrawn his request for asylum after the Russian leader said he should stop "harming our American partners".

World's protection

But while country after country denied his asylum requests on technical grounds, Venezuela, part of an alliance of leftist governments in Latin America, said it was time to stop berating a man who has "done something very important for humanity".

"He has a right to protection because the United States in its actions is persecuting him ... Why are they persecuting him?

Nicolas Maduro, Venezuelan president

"He deserves the world's protection," President Nicolas Maduro told Reuters during a visit to Moscow for a meeting of gas exporting countries.

"He has a right to protection because the United States in its actions is persecuting him ... Why are they persecuting him? What has he done? Did he launch a missile and kill someone? Did he rig a bomb and kill someone? No. He is preventing war."

Maduro said he would consider an asylum application. He later had talks with Putin but neither leader said whether they had discussed Snowden.

Snowden's request for safety in Ecuador, which has sheltered the founder of antisecrecy group WikiLeaks Julian Assange in its London embassy for more than a year, has seemingly ended.

Ecuador's President Rafael Correa said on Sunday that Snowden's fate was in Russia's hands because Ecuador could not consider the plea until he reached his country's territory or one of its embassies.

Bolivian President Evo Morales, also in Moscow for the gas conference, told Russia's RT television that his country would consider an asylum request but had not yet received one.