The United Nations human rights office has asked the Nicaraguan government to open all prisons to monitors and called for a halt to violence that has killed more than 280 people in three months of unrest.
UN human rights spokesman Rupert Colville on Tuesday asked the government to provide information on two activists who have been missing since they were detained at an airport in Nicaragua last week.
At a press briefing, he said the violence in the Central American country had been "overwhelmingly perpetrated" by the Nicaraguan state and loyal armed groups.
On Monday, UN Chief Antonio Guterres called for an "immediate halt" to violence.
"It's evident that there is a shocking number of deaths and a lethal use of force by entities tied to the state that is unacceptable," Guterres said at a news conference in neighbouring Costa Rica.
International condemnation
International criticism of President Daniel Ortega has been growing in recent days.
The US Department of State issued on Monday a statement condemning attacks "by Daniel Ortega's para-police against university students, journalists, and clergy across the country" and calling on Ortega to "cease his repression of the people of Nicaragua" immediately.
The European Union called violence against civilians and delays in providing medical assistance to the wounded "deplorable".
In a statement issued on Sunday, an EU foreign affairs spokeswoman said, "We expect the authorities to ensure the security of the population and the respect for fundamental rights,"
Hundreds of protesters gathered in the Nicaraguan capital of Managua on Monday to demand justice for victims of a crackdown on demonstrations against Ortega, which claimed at least 12 lives over the weekend.
At least 10 people, including a young girl, were killed on Sunday after pro-government forces launched an operation in and around the city of Masaya, a rights group said.
The violence came a day after 200 university students were freed from a besieged church in Managua after a 16-hour ordeal in which two were killed.
More than 280 people, the vast majority of them civilians, have been killed in the political unrest since protesters took to the streets in mid-April over now-scrapped pension reforms.
Protesters have since expanded into a general opposition to President Daniel Ortega and his government, which opponents call a dictatorship characterised by nepotism and brutal repression.
Earlier this month, Ortega rejected calls for his resignation, telling thousands of supporters that protesters demanding he leave office should "seek the vote of the people" if they want to govern.
Rights groups have accused security forces and groups loyal to the government of using "lethal force" to crack down on the protests.
