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.
FBI foils "terror plot" targeting Los Angeles
Four people are facing criminal charges in connection with what Attorney General Pam Bondi described on Monday as a foiled bomb plot that contemplated multiple targets, including US immigration agents and their vehicles.
Hong Kong court finds tycoon Jimmy Lai guilty in landmark security trial
Hong Kong's High Court on Monday found pro-democracy campaigner Jimmy Lai guilty of conspiracy to collude with foreign forces and to publish seditious material under a China-imposed national security law that could see him jailed for life.
Ukraine peace talks stretch into second day at start of pivotal week for Europe
Ukrainian President Volodymyr Zelenskyy will resume talks with US President Donald Trump's envoys in Berlin on Monday, after the US side said a "lot of progress" had been made on ending Europe's deadliest conflict since World War II.
Flash floods kill at least 37 people in Morocco's Safi province
At least 37 people have been killed in flash floods triggered by torrential rains in Morocco's Atlantic coastal province of Safi, Moroccan authorities said on Monday.
'Hero' who disarmed Bondi gunman recovering after surgery, family says
A Sydney resident who wrestled a gun from one of the alleged attackers during the mass shooting at Bondi Beach is recovering in hospital after undergoing surgery for bullet wounds to his arm and hand, his family said.
