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.
Israel warns Lebanon of 'heavy price' as week's death toll nears 300
Israel has warned Lebanon of a "very heavy price" if it did not rein in Hezbollah on Saturday, as it pounded the group's strongholds around the country with air strikes and mounted a deadly airborne raid in the east.
Israeli settler fatally shoots Palestinian in West Bank
An Israeli settler has shot dead a 27-year-old Palestinian man in the occupied West Bank on Saturday, the Palestinian Health Ministry said.
Israel carries out rare airborne raid in Lebanon; 16 killed in strikes
Israel launched airstrikes targeting Lebanon's Nabi Chit and nearby towns on Saturday, killing at least 16 people Lebanon's health ministry confirmed.
US skips congressional review to approve arms sale to Israel
The US State Department said on Friday it has approved a sale worth $151.8 million to Israel for munitions and munitions support, without submitting it for congressional review.
Flash floods in Nairobi kill 23, disrupt flights at major airport
Flash floods across Nairobi overnight has left at least 23 people dead, authorities said, adding that dozens of cars were swept away and flights at East Africa's biggest airport disrupted.
Dubai authorities have confirmed that debris from an aerial interception fell onto a vehicle in the Al Barsha area, resulting in the death of a driver.
The UAE's Ministry of Defence has announced on Saturday night that it is currently responding to missile and drone threats.
President His Highness Sheikh Mohamed bin Zayed Al Nahyan said the UAE will "emerge stronger than before", affirming that the safety and security of citizens, residents, and visitors remain a top priority.
