Nicaragua has released 222 of the 245 opposition prisoners it was holding.
The freed prisoners, who are critics of President Daniel Ortega, were deported to the United States.
The US state department welcomed the move, which it said had been made “unilaterally” by the Nicaraguan government.
Among those freed are opposition politicians who had planned to run against Mr Ortega in the 2021 election but who were jailed in its run-up.
With his fiercest opponents in prison, Mr Ortega won a fourth consecutive term in the election. He has been in power without interruption since 2007.
In an interview for US Spanish language network Telemundo, US President Joe Biden said he did not know whether this meant Nicaragua was ready to change its policies on human rights, but said: “We’re happy to receive them and I’m glad they’re out.”
Mr Ortega said on local TV that the released prisoners were “agents” of foreign powers and sought to undermine national sovereignty. “Let them have their mercenaries,” he said, quoted by Reuters news agency.
Nicaraguan opposition sources said that those freed have been stripped of their Nicaraguan nationality and an official from the Nicaraguan judiciary described them as “traitors” who had been deported.
Among the prisoners released was opposition leader Juan Sebastian Chamorro and former presidential hopeful, Felix Maradiaga, who said he learned he had been stripped of his citizenship shortly after arriving in the US.
“I will be Nicaraguan until the day I die. I will still love Nicaragua, not just as the country where I was born but also as the land I wish to see have democracy” he told reporters.
The Biden administration, which described the 2021 election in Nicaragua as “a pantomime”, had been pressuring the Nicaraguan government to release the prisoners. The US said they had been arbitrarily detained.
The US state department said that the US had helped arrange their charter flight to Dulles airport, near Washington DC.
“Some of these individuals have spent years in prison, many of them for exercising their fundamental freedoms, in awful conditions and with no access to due process,” it said in a statement.
Other members of the influential Chamorro family, which has long opposed the government of President Ortega, were among those released.
Juan Sebastian Chamorro’s cousin Cristiana, whose mother Violeta defeated Daniel Ortega in the 1990 election, was one of those who had planned to stand against Mr Ortega in the 2021 polls.
She was seen by many in the opposition as their best hope of defeating Mr Ortega.
But shortly after she announced she would run for president, prosecutors accused her of money laundering. She was subsequently sentenced to eight years in prison.
She was deported along with her brother, Pedro Joaquín Chamorro, who was also sentenced last year.
A student opposition umbrella group, Nicaraguan University Alliance, said two of its members, Lesther Alemán and Max Jerez, were also on board the plane headed to the US.
Students were at the forefront of anti-government protests which rocked Nicaragua in 2018 and the two student leaders remained vocal critics of the government led by President Ortega and his wife, Vice-President Rosario Murillo, until their arrest in 2021.
Members of the Nicaraguan University Alliance said they would continue to fight for the rights of those sent to the US so that they “can return from exile and exercise their rights fully”.