Venezuela's state TV has shown a video of a US citizen apparently confessing to plotting to overthrow President Nicolás Maduro and bring him to the US.
Luke Denman is one of 13 people arrested over the weekend. Venezuela says they are "mercenaries" whose armed incursion was foiled.
Mr Maduro has often accused US President Donald Trump of trying to invade the country and overthrow him.
Mr Trump earlier this week denied any US involvement.
Secretary of State Mike Pompeo has said the US government will use "every tool" to secure the return of the Americans.
What did Venezuelan TV broadcast?
In Wednesday's video, Mr Denman, 34, appeared to explain that he was hired to train Venezuelans in Colombia before returning to Caracas and taking control of an airport to allow Mr Maduro to be taken out of the country.
"I was helping Venezuelans take back control of their country," Mr Denman, a former special operations forces member, is seen as saying.
Mr Denman said he and Airan Berry, 41, were contracted by Jordan Goudreau, an American military veteran who leads a Florida-based Silvercorp USA firm, to carry out the operation.
Venezuela said it would seek extradition of Mr Goudreau, who has admitted he was involved in the operation.
According to Mr Maduro, Silvercorp signed a contract with opposition leader Juan Guaidó, a politician seen by the US and many European countries as Venezuela's legitimate leader.
"Donald Trump is the direct chief of this invasion," Mr Maduro said during a press conference, after the video of Mr Denman was broadcast.
The Venezuelan president said the Americans would have a fair trial.
He did not provide any information as to the whereabouts of the detained men. It is unclear if they have access to a lawyer.
Who are the detained US citizens?
Not much is yet known about Mr Denman and Mr Berry.
Venezuelan military high command have said the pair are members of the US security forces. US media have suggested they are former members – but this has not been confirmed.
Caracas says that 11 other people were arrested, and eight armed men killed during the alleged coup attempt.
What is the background to this?
Mr GoudrRead More – Source