US President Barack Obama insisted Thursday he would not let the fate of fugitive intelligence leaker Edward Snowden ruin ties with Russia and China as Washington bluntly warned Ecuador not to give him asylum.

Snowden, wanted by the US authorities for leaking sensational details of vast US surveillance programmes, is said by the Kremlin to have been in the transit zone of Moscow's Sheremetyevo airport since arriving on a flight from Hong Kong Sunday.

But in a mystery that has captivated the world, there has not been a single sighting of him at the airport and his travel plans remain an enigma after he failed to board a flight to Havana on Monday.

Ecuador, seen as his most likely eventual destination, denied Thursday it had given him a "safe passage" document and said it would not be able to process his asylum request until he enters Ecuadorian territory.

The affair has however triggered a war of words between the US and Ecuador, and risks further ratcheting up tensions between Washington and Moscow, as well as Beijing, which are already strained by the conflict in Syria.

But Obama insisted the United States -- which has revoked Snowden's passport -- would not scramble jets to intercept him should he fly from Russia.

"I am not going to be scrambling jets to get a 29-year-old hacker," Obama said on a visit to Senegal, giving the wrong age for the 30-year-old former National Security Agency (NSA) technician.

Obama indicated he did not want to ruin ties with Moscow and Beijing for the sake of Snowden, saying their relationships were broad and ranged over many issues.

He also rejected any "wheeling and dealing" over Snowden and said he had not called President Xi Jinping of China or Russian President Vladimir Putin to discuss the issue.

"The reason is, number one, I shouldn't have to. This is something that routinely is dealt between law enforcement officials in various countries," said Obama.

Putin has indicated that Moscow is keen to see the back of its unexpected visitor, while also strongly rejecting US pressure to hand over Snowden as the two countries have no extradition treaty.

"The sooner this (he flies onwards from Moscow) happens, the better," said Foreign Minister Sergei Lavrov.

Ecuador, whose embassy in London is giving refuge to WikiLeaks founder Julian Assange as he faces extradition to Sweden on allegations of sexual assault, has said it is considering an asylum request from Snowden.

And on Thursday it defiantly dropped out of a trade pact with the United States, claiming it had become an instrument of "blackmail."

The US responded by telling Quito it wanted to maintain a good economic relationship but warned that granting asylum to Snowden would have "grave difficulties" for bilateral ties.

Countering claims by WikiLeaks, Ecuador's Political Issues Minister Betty Tola denied that the government had authorised the delivery of any "safe passage or refugee document" that would allow Snowden to travel to the country.

--- 'Almost certainly grant asylum' ---

Ecuadoran Foreign Minister Ricardo Patino has said it could take weeks to decide whether to grant asylum to Snowden.

Venezuelan President Nicolas Maduro said that Caracas would "almost certainly" grant political asylum to Snowden if he applied.

Maduro, who like Ecuador President Rafael Correa is a leftist anti-American populist, is by coincidence expected in Moscow next week for an energy summit.

Snowden had been expected to leave Moscow on an Aeroflot flight on Monday to Havana, where he could have caught a connection to Quito, but he did not appear on the plane and did not take other flights this week.

The next Moscow-Havana flight is on Saturday but there have been no reports he has a booking.

And a source quoted by Russia's RIA Novosti state news agency said Snowden cannot currently leave the transit zone.

"Snowden does not have valid documents. He is not flying to Cuba or anywhere else for that matter," the source said.

Another source quoted by Interfax said the situation was at a "dead end" and there would only be a breakthrough when a third country formally offered Snowden asylum.

The confusion has raised the prospect that Snowden could be in limbo for weeks or even months while a solution is found.

Putin has also denied suggestions that Russia could be holding up Snowden deliberately to allow an extensive debriefing at the hands of Russian special services.

Snowden abandoned his high-paying intelligence contractor job in Hawaii -- which he himself described as "living in paradise, making a ton of money" -- and went to Hong Kong on May 20.

He then began issuing a series of leaks on the NSA gathering of phone call logs and Internet data, triggering concern from governments around the world.

He arrived in Moscow on Sunday on an Aeroflot flight from Hong Kong, a special administrative region under Chinese rule, prompting anger from Washington over how the local authorities there allowed Snowden to travel.

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