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.
Rescuers search for 130 people after Indonesia passenger ship sinks; six dead
Indonesian rescuers were searching on Sunday for 130 people from a passenger ship that sank in the Java Sea after 113 others were evacuated, the country's search and rescue agency said, adding that six people had died.
Russian drone attack injures five in Ukraine's Odesa, officials say
At least five people were wounded in a Russian attack on the Ukrainian city of Odesa on Sunday morning, officials said, a day after strikes on the city killed two people.
Philippine ferry fire victims may take months to identify, authorities say
Authorities in the Philippines said on Sunday it could take weeks or months to identify the victims of a ferry fire that killed 76 people, as forensic experts begin collecting and comparing DNA samples and investigators determine the cause.
Israeli strike kills two people in Gaza, medics say
An Israeli airstrike on Sunday killed at least two Palestinians in a vehicle and wounded 13 others in the Gaza Strip, medical staff said.
Saudi Arabia shuts key oil pipeline after drone attack
Saudi Arabia shut its East-West oil pipeline on Friday after it was hit in a drone attack, disrupting a key route used to bypass shipping problems in the Strait of Hormuz.
His Highness Sheikh Hamdan bin Mohammed bin Rashid Al Maktoum, Crown Prince of Dubai and Deputy Prime Minister, has approved an official of the rank of Director-General as the first recipient of the Mohammed bin Rashid Leadership Medal.
Dr Anwar Gargash, diplomatic advisor to the UAE president, on Sunday said the meeting between Abu Dhabi Crown Prince His Highness Sheikh Khaled bin Mohamed bin Zayed Al Nahyan and Iranian President Dr Masoud Pezeshkian reflects the UAE's stance of "deterrence and diplomacy".
The UAE has strongly condemned the drone attack on Saudi Arabia's East-West oil pipeline in the Riyadh and Medina regions.
