At least 42 inmates have been found dead at four prisons in the capital of Brazil's northern Amazonas state on Monday.
Authorities said the victims appeared to have been killed by "asphyxiation" and were discovered during routine inspections at the prison facilities.
Additional reinforcements have been dispatched to boost security, they added, without providing more details.
This comes a day after 15 prisoners were killed in gang clashes in the same city.
UN chief calls New START treaty expiration 'grave moment'
United Nations Secretary-General Antonio Guterres has called the expiration of the New START Treaty a grave moment for international peace and urged Russia and US to negotiate a new nuclear arms control framework without delay.
Pakistan military says it concludes week-long fight against Baloch separatists
Pakistan's military said on Thursday it had concluded a week-long operation against separatists in Balochistan who stormed more than a dozen locations, taking hostages, setting off explosives and waging gun battles with security forces.
One dead, one missing as Storm Leonardo batters Portugal and Spain
One man died in Portugal after flood waters engulfed his car and in Spain, a girl was dragged away by a river after trying to rescue her dog, as Storm Leonardo lashed the Iberian peninsula with heavy rains and strong winds on Thursday.
Freezing rain causes cancellations, delays at Berlin airport
Snow and freezing rain hit Berlin's airport on Thursday morning, causing airlines to delay or cancel multiple departing flights.
700 immigration agents withdrawn from Minnesota
The Trump administration is withdrawing some 700 federal immigration enforcement agents from Minnesota, although about 2,000 agents will stay in place, White House border czar Tom Homan announced on Wednesday, a number the state's Democratic leaders say is still too high.
