Washington wants Snowden, currently in limbo in Moscow, arrested for disclosing details of the massive US electronic intelligence operations around the world.
Venezuela, Bolivia and Nicaragua, all run by leftist governments, have offered Snowden asylum. The 30-year-old US fugitive however told rights activists in Moscow yesterday that he would seek interim refuge in Russia.
Four European countries also came under attack in Montevideo at a summit of Mercosur, the regional bloc, for shutting off their airspace and holding up a plane carrying Bolivian President Evo Morales, apparently on suspicion that Snowden was aboard.
The Mercosur leaders issued a statement reaffirming "the inalienable right of every state to grant asylum," a right which, they said, "must not be restricted or curbed".
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"It is fundamental to ensure that the right of asylum seekers to travel safely to the country granting asylum be guaranteed," they added, in a thinly veiled reference to US pressure to block Snowden's possible departure from Russia to Venezuela.
They demanded "an immediate end to such practices and explanations as to their motivation and their consequences."
They also plan to push for the adoption of Internet regulatory rules, with an emphasis on cyber-security "to guarantee the protection of communications and preserve the sovereignty of states."
Snowden has been stranded at Moscow's Sheremetyevo Airport since arriving on a flight from Hong Kong on June 23. His US passport has since been revoked.
Mercosur leaders also said they would recall their ambassadors from Spain, France, Italy and Portugal for consultations in protest at the four nations' decisions to close their airspace to the plane carrying Morales last week.