The Organization of American States said on Tuesday that Nicaragua was experiencing a "critical human rights situation" that had upset the country's constitutional order, following President Daniel Ortega's crackdown on opponents.
Major demonstrations last year left some 300 people dead.
Protests - including two hunger strikes by mothers of detained activists - have started up again in recent days, leading to clashes with Ortega supporters and arrests.
The report by a commission of the Washington-based OAS followed United Nations criticism earlier in the day of the arrest of 16 anti-government protesters on charges it said seemed "trumped-up."
The OAS recommended a special session of its general assembly be convened immediately to review affairs in the country.
"It is clear that Nicaragua is experiencing a critical human rights situation that urgently demands the attention of the Inter-American community and the world at large," the OAS said.
The Nicaraguan government did not immediately respond to a request for comment. It has previously dismissed the creation of the OAS commission, viewing it as an attempt to interfere in its affairs.
On Monday, Nicaraguan authorities said the 16 detainees were suspected of planning terrorist attacks in the Central American country.
Those detained include prominent student protesters such as Nicaraguan and Belgian national Amaya Coppens, who has been arrested previously.
Rupert Colville, a spokesman in Geneva for the U.N. High Commissioner for Human Rights, told reporters the arrests looked like an attempt to silence criticism of the government.
"We are very concerned that these apparently trumped-up charges may constitute a renewed attempt to stifle dissent," said Colville.
He also urged the government to respect the rights of a separate group of hunger strikers in Managua's cathedral.
The Roman Catholic Church on Monday accused groups linked to the government of beating a priest and violently taking control of the cathedral.
"We condemn these acts of desecration, harassment and intimidation, which are not contributing to the peace and stability of the country," the Church said in a statement.
On Monday, seven mothers of people detained earlier by authorities had said they would begin a hunger strike in the cathedral to demand the release of their children before Christmas.
Colville said everyone who may have been "arbitrarily detained" in the country should be released.
"The government must end the persistent repression of dissent and the ongoing pattern of arbitrary arrests," he said.