Felix Maradiaga and Juan Sebastian Chamorro are opposition politicians seeking to run against Ortega in November's elections as he vies to keep the office he has held since 2007.

Their arrests follow those of opposition politicians Arturo Cruz and Cristiana Chamorro in recent days.

Maradiaga, 44, an academic and businessman, had been notified that he was being investigated in a hearing at the attorney-general's office on Tuesday.

"I am going to stay in the running for the presidential candidacy," Maradiaga said after the meeting. Minutes later, he was arrested.

Juan Sebastian Chamorro, a cousin of Cristiana Chamorro, was arrested later on Tuesday.

Separate police statements on the Tuesday arrests listed the same reasons for the detentions, including accusations of working with foreign financing to carry out "acts of terrorism and destabilisation", but without details.

They also accused the two opposition contenders of requesting foreign interference in internal affairs and military intervention.

Leftist Ortega, 75, was first president in the 1980s, returned to power in 2007, and since governed three straight terms.

International organisations, including the Inter-American Commission on Human Rights and the Office of the United Nations High Commissioner for Human Rights, have accused Ortega's government of fabricating false accusations against opponents.

Australian Associated Press