The Organization of American States puts the death toll at 317 from more than three months of anti-government protests in Nicaragua.
The OAS's human rights branch said Thursday that 23 minors and 21 policemen are among the dead.
It again called on the Nicaraguan government to "fulfill its international obligations concerning human rights" and "promptly and seriously investigate each of these crimes."
It also says many of those who have been arrested were not informed of their rights or told of the specific charges against them.
Protests exploded in April when President Daniel Ortega announced changes in the country's popular pension system.
He soon gave up his plans, but the protests continued along with the government's violent crackdown. The government puts the death toll at just under 200.
Ortega has rebuffed the church's call for talks with the opposition and is refusing to hold early elections. He says the demonstrators are terrorists and accuses them of plotting a coup.
The United States has imposed sanctions and visa restrictions against Nicaraguan officials it says are responsible for the violence and warns more sanctions could be on the way.