"They are convicts, confessed, caught red-handed and are being judged by the republic's attorney general, by Venezuela's civil courts, and the process will be full of guarantees and fair," said Maduro.

The socialist leader insisted the Americans, previously identified as Luke Denman and Airan Berry, were being "well treated, with respect."

Venezuela announced on Monday it arrested the pair on suspicion of trying to topple Maduro as part of a mercenary invasion force supported by the US-backed opposition.

Maduro showed the passports of Denman, 34, and Berry, 41, on state television and claimed they were members of the US security forces.

US President Donald Trump denied his administration had anything to do with the mission while Washington accused Maduro of launching a "disinformation campaign."

Earlier Wednesday, however, US Secretary of State Mike Pompeo said Washington would "use every tool that we have available to try to get them back."

Venezuela's Attorney General Tarek William Saab had said on Monday that opposition leader Juan Guaido, who is backed by the US and more than 50 countries, had signed a $212 million contract with "hired mercenaries" using funds seized by the United States from the state oil company PDVSA.