Nicaragua says the recently detained opposition figures are "usurpers" funded by the United States to overthrow President Daniel Ortega.
The opposition figures received "millions of dollars in cash from the American public through USAID," the government said in a document on Monday.
Nicaragua arrested five opposition figures over the weekend on charges of "inciting foreign intervention," bringing to 13 the number of dissidents detained since June 2. Four presidential hopefuls are among the detainees, including Cristiana Chamorro, the daughter of former president Violeta Barrios de Chamorro.
The Sunday arrests included four from the Unamos opposition party, which is largely made up of dissidents who split from Ortega's Sandinista National Liberation Front (FSLN) as they disagreed with his leadership.
Julie Chung, the top US diplomat for Latin America, described the arrests as "arbitrary" and criticized what she called Ortega's "campaign of terror."
"OAS (Organization of American States) members must send a clear signal this week: enough repression. The region cannot stand by and wait to see who is next," the US envoy tweeted on Sunday.
On June 9, the US slapped sanctions on four top Nicaraguan officials over the latest crackdown.
Washington has imposed sanctions against Nicaragua’s government and Ortega's inner circle since 2018 when deadly protests engulfed the country.
Ortega, 75, served as president from 1979 to 1990, and was inaugurated, once again, in 2007 and won two consecutive terms in office since then.
He did not announce his intention to run for a fourth term, but reports say he is widely expected to seek a new term in the November 7 elections.
The United States has long maintained an interest in interfering in the internal affairs of Nicaragua, a Latin American country it once occupied from 1912 to 1933 as part of the Banana Wars.