Five presidential hopefuls have been arrested in a sweeping crackdown by President Daniel Ortega ahead of elections in November.
Miguel Mora was the 17th major opposition figure to have been held this month, with two more rounded up on Monday.
Several hundred people have been behind bars since anti-government protests broke out across the Central American country in 2018, with protesters calling Ortega a dictator and demanding he stands down.
- 2021: Pre-election arrests -
The roundup of Ortega's possible challengers in the November presidential election began on June 2 when Cristiana Chamorro, the daughter of former president Violeta Barrios de Chamorro, was placed under house arrest.
Days later three other opposition candidates were arrested: the economist Juan Sebastian Chamorro Garcia -- Cristiana's cousin -- Felix Maradiaga and former diplomat Arturo Cruz.
- 'Dictator' -
Washington and the UN called for their release, with top US diplomat for Latin America, Julie Chung, tweeting the arrests "should resolve any remaining doubts about Ortega's credentials as a dictator."
On Sunday a fifth would-be candidate, Mora, was arrested at his home for "inciting foreign interference in internal affairs and requesting military intervention."
The government claims those it has held are "usurpers" funded by the US to topple Ortega, who governed Nicaragua from 1979 to 1990, returned to power in 2007 and who has won two successive re-elections since then.
The leader of the 1979 Sandinista revolution is widely expected to seek a fourth term in the November, though he has not yet confirmed that he will stand.
- 2020: 'Repressive' law -
Those detained this month have been accused under a law approved by parliament in December purporting to defend Nicaragua's "sovereignty", which has been criticized by rights bodies as a means of freezing out and jailing challengers.
- 2018: Bloody protests -
Mora, a journalist, had been previously detained in 2018 as part of a crackdown on massive anti-Ortega protests that left 325 dead. More than 100,000 Nicaraguans have since fled the country.
The protests were triggered by a now-scrapped pension reform plan with demonstrators accusing Ortega and his wife Rosario Murillo, the vice president, of establishing a corrupt and nepotistic dictatorship.
- Sanctions -
The United States imposed sanctions on Ortega's government and inner circle during the 2018 demonstrations.
On June 9, amid the latest round of arrests, the US imposed fresh sanctions against three Nicaraguan officials and the president's daughter, while accusing the regime of undermining democracy and abusing human rights.
Luis Almagro, secretary-general of the Organization of American States, urged the release of all "political prisoners in Nicaragua," adding that "the harassment and oppression of the dictatorship of... Daniel Ortega must stop."