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.
Indonesia calls off search for journalists missing while covering eruption
Indonesian rescuers have called off a search on its 10th day for eight people missing at sea, including five journalists who were covering the eruption of Mount Anak Krakatau earlier this month.
Gaza building collapse: Rescue efforts end after 45 saved
Gaza rescuers wrapped up searches on Thursday in the rubble of a bomb-damaged building that collapsed a day earlier, where 21 people were killed and 45 rescued from under the rubble, a Palestinian official said.
US officials made rare Myanmar visit to free American businessman
A delegation of US officials travelled to Myanmar this week and met with the country's military-backed government to secure the release of detained US citizen Adam Castillo, a Department of State spokesman said on Thursday.
Trump derides EU pitch to Canada as 'laughable', threatens more tariffs
US President Donald Trump has threatened to take action against the EU if it moves forward with European Commission President Ursula von der Leyen's proposal to make Canada the bloc's first associate member.
Australia cracks down on student and backpacker visas to curb migration
Australia will stop foreign students from bringing partners and children to accompany them while they study and tighten working holiday visa rules, a senior minister said on Thursday, amid growing debate over high migration levels.
The UAE Ministry of Interior has announced the arrest of the leader of an international criminal gang in a joint operation with Swedish authorities.
The UAE has delivered its sixth humanitarian aid aircraft to Nepal, carrying 25 tonnes of food supplies and clothing for communities affected by recent floods and landslides.
The UAE is marking the 52nd anniversary of His Highness Sheikh Hamad bin Mohammed Al Sharqi's accession as Ruler of Fujairah.
