Felix Maradiaga, presidential pre-candidate for the Blue and White Alliance (UNAB) Photograph:( AFP )
Last week, two other opposition politicians planning to run against Ortega, branded a 'dictator' by the United States were detained.
Nicaraguan authorities on Tuesday detained two more potential presidential candidates, for a total of four, as a crackdown by President Daniel Ortega deepened ahead of elections later this year.
Felix Maradiaga was held after appearing at the public ministry where prosecutors are investigating him for alleged acts against sovereignty, terrorism and backing international sanctions against the government.
And Juan Sebastian Chamorro Garcia, the cousin of another detained candidate, Cristiana Chamorro, was arrested for "inciting foreign interference in internal affairs" and the "organization with funding from foreign powers to perpetrate terrorist acts," according to a police statement.
Last week, two other opposition politicians planning to run against Ortega, branded a "dictator" by the United States were detained.
Cristiana Chamorro was placed under house arrest on government allegations of money laundering, while Arturo Cruz was held in pre-trial detention so prosecutors can investigate allegations of "provocation... and conspiracy to commit harm to national integrity."
Maradiaga, 44, faces some of the most serious allegations.
Police said, "he is being investigated for carrying out acts that undermine independence, sovereignty, and self-determination, inciting foreign interference in internal affairs, and calling for military interventions."
He is also accused of using "financing from foreign powers to carry out acts of terrorism and destabilization," the police added.
The charges against Maradiaga are related to a law approved in December by the legislature, dominated by Ortega allies, supposedly to defend "sovereignty" against hostile foreign influence.
Critics say it is aimed at preventing opposition politicians from standing in the election, set for December 7.
Sponsored by leftist Ortega, it bars "those who ask for, celebrate and applaud the imposition of sanctions against the Nicaraguan state."
Before his arrest, Maradiaga said he had "nothing to hide" and that he wanted to call for sanctions against those "who have committed crimes against humanity," not against his whole country.
Ortega, an ex-guerrilla who governed from 1979 to 1990, returned to power in 2007 and won two successive reelections.
But he has been accused by the opposition and NGOs of authoritarian rule and the brutal suppression of demonstrations against his rule.
Both the European Union and the United States have imposed sanctions against Ortega and his government.
"Presidential candidate Felix Maradiaga's arbitrary arrest ... should resolve any remaining doubts about Ortega's credentials as a dictator," said Julia Chung, the top US diplomat for Latin America.