It's still unclear whether European countries did block the plane and, if so, why. French, Spanish and Portuguese officials all said yesterday the plane was allowed to cross their territory.

Low on fuel, the plane's crew eventually won permission to land in Vienna, where the drama continued yesterday.

Bolivia accused Austria of "kidnapping" its president after authorities searched his plane during the stopover.

Bolivian foreign minister David Choquehuanca, said after the plane touched down in Vienna: "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 Snowden was on the plane."

He added: "We don't know who invented this big lie. We want to express our displeasure because this has put the president's life at risk."

Defence minister Rubin Saavedra, who was on the plane with Morales, accused the Obama administration of being behind the action by France and Portugal, calling it "an attitude of sabotage and a plot by the government of the United States".

Morales lashed out at European countries for denying his jet entry into their airspace overnight. "I am not a delinquent," Morales said at Vienna airport.

Morales flew out of Austria yesterday after police inspected his jet and found Snowden was not on board.

Calling it "an act of aggression", Bolivia's UN envoy Sacha Llorenti said the country would file a complaint to UN chief Ban Ki-moon over the diversion which he said "violated international law".

He said in Geneva: "We're talking about the president on an official trip, after an official summit, being kidnapped."

The Austrian interior ministry said airport police carried out a "voluntary inspection" of the jet.

French government spokeswoman Najat Vallaud-Belkacem said France "ended up authorising the flight over its airspace by Mr Morales' plane", but wouldn't explain whether there had been an initial refusal.

The Portuguese Foreign Ministry said Portugal had granted permission for the plane to fly through its airspace but declined Bolivia's request for a refuelling stop in Lisbon due to unspecified technical reasons.

Bolivia said Spain agreed to allow the plane to refuel in the Canary Islands - but only if Bolivian authorities allowed it to be inspected. Spanish Foreign Minister Jose Manuel Garcia-Margallo denied his country demanded an inspection of the plane.

Morales was at an energy conference in Moscow on Monday when asked if he would consider giving Snowden asylum.

The 30-year-old has been holed up at Sheremetyevo Airport in Moscow for more than a week and his passport has been revoked by the United States.

"Yes, why not?" Morales responded. "Of course, Bolivia is ready to take in people who denounce - I don't know if this is espionage or monitoring. We are here." He said Bolivia had not received a request for asylum from Snowden, despite news reports to the contrary.

There was plenty of confusion in Moscow over how Snowden could possibly have left undetected on a government aircraft.

Government planes carrying foreign officials to diplomatic meetings in Moscow typically arrive and depart from Vnukovo Airport.

This is the main airfield used by the Russian government, rather than Sheremetyevo, where Snowden arrived from Hong Kong on June 23 hours after US officials had sought his extradition there.

The speculation that Snowden would hitch a ride on a government jet was discounted by the fact that the plane would have to first make a quick flight from one Moscow airport to the other.