The arrests beginning late on Saturday marked a deepening political crisis in the Central American nation, before an election in November in which the leftist Ortega, 75, is seeking to extend his 14 years as president.

In the past few weeks, a dozen opposition figures have been arrested on orders from Ortega's security apparatus, including four declared presidential rivals.

Ortega loyalists argue they are only enforcing the law, which prohibits would-be candidates from receiving foreign financing or the publication of information the government determines to be false.

Police blamed the detainees for seeking to undermine the country's independence and sovereignty, as well as for "inciting foreign interference in internal affairs".

The latest raids targeted the leadership of the leftist opposition Unamos party, including its president, Suyen Barahona, and former general Hugo Torres.

Unamos is made up of many former Ortega allies like Torres, who fought alongside him in the late 1970s as they drove right-wing dictator Anastasio Somoza from power.

Just before he was arrested, the 73-year-old Torres uploaded a video that denounced Ortega for launching a "second dictatorship" and betraying the values he once championed.

"These are desperate acts from a regime that can feel itself dying," he said.

Last week, a senior US diplomat blasted the "wave of repression" by Ortega and his allies, adding the United States was prepared to review trade relations with Nicaragua if the upcoming election was not free and fair.

Earlier this month, police placed opposition leader Cristiana Chamorro under house arrest shortly after she announced a presidential run, seeking to end Ortega's three consecutive terms in office.

Australian Associated Press