A former Honduran president convicted of helping to smuggle 400 tons of cocaine into the United States has left prison after being pardoned by President Donald Trump, his wife said Tuesday.

Juan Orlando Hernandez was released from a West Virginia prison on Monday and was "once again a free man," his wife announced on social media. He had been sentenced last year to more than four decades behind bars.

Trump's pardon – issued as the US military carries out a controversial campaign against alleged drug traffickers in Latin America – has provoked fierce criticism from his political opponents and bewilderment by some allies.

On Tuesday, Trump responded to the criticism by downplaying Hernandez's involvement in the drug trade.

"Well, he was the president, and they had some drugs being sold in their country. And because he was the president, they went after him," Trump told reporters, calling it a "horrible witch hunt" and saying he feels "very good about" the pardon.

"If you have some drug dealers in your country and you're the president, you don't necessarily put the president in jail for 45 years," Trump said.

The ex-president's release also comes as Hondurans await final results from Sunday's razor-close presidential election, in which Trump backed the candidate of Hernandez's right-wing party.

Hernandez's pardon came as a surprise, given Trump has made an ostensible war against Latin American drug trafficking a centrepiece in his turbulent second term.

A large contingent of US military forces are deployed in the Caribbean to pressure Venezuela's leader Nicolas Maduro, whom the Trump administration has designated as part of a drug cartel.

US forces are regularly blowing up small boats alleged to be carrying drugs, despite international experts saying the strikes amount to extrajudicial killings.

Hernandez led the Central American nation from 2014 to 2022.

He was accused by US prosecutors of years-long efforts to aid drug cartels, including Mexico's Sinaloa Cartel – designated by the Trump administration this year as a terrorist organisation.

Hernandez was extradited just weeks after leaving office, convicted and sentenced to 45 years in prison.

Democrats rebuked the Republican president, accusing him of hypocrisy in claiming to have stepped up the fight against the flow of illicit drugs into the United States while freeing a man convicted of using his office to aid drug traffickers.

Senator Dick Durbin, the top Democrat on the Senate Judiciary Committee, said evidence presented at Hernandez's trial had established that the former president had "orchestrated a vast trafficking conspiracy" that raked in millions of dollars for drug cartels.

"This is not an action by a president trying to keep America safe from narcotics," Durbin said.

"It is a strange understanding of his power that he would use this and not penalise those responsible for the narcotics coming into the United States."

Senator Bill Cassidy, from Trump's Republican Party, also slammed Trump's move.

"Why would we pardon this guy and then go after Maduro for running drugs into the United States?" he asked on X.

White House Press Secretary Karoline Leavitt on Monday defended Trump, depicting Hernandez as the victim of prosecutorial overreach under former president Joe Biden. (Agencies)