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.
Americans mark 25 years since September 11 attacks amid grief, reflection
Twenty-five years after the deadliest attack on US soil, Americans paused on Friday to commemorate the nearly 3,000 people killed when hijacked planes slammed into the World Trade Center, the Pentagon and a field in Pennsylvania.
Nigeria parliament boycotts South Africa events over anti-migrant attacks
Nigeria's parliament has suspended official visits to South Africa and ordered lawmakers to boycott South African-hosted legislative activities, citing reports of attacks on Nigerians and other African migrants there.
Sydney Airport flights disrupted due to air traffic controller shortage
A shortage of air traffic controllers has caused flight cancellations and major delays at Sydney Airport on Friday morning, the federal agency responsible for managing Australia's air traffic said.
Philippine firefighters enter charred ferry as search continues for dozens missing
Philippine firefighters on Friday managed to board a burned-out ferry more than a day after the ship caught fire on its way from Manila to the western province of Palawan, killing five people and leaving more than 80 missing.
Modi, Putin hold talks in New Delhi on trade, defence
Indian Prime Minister Narendra Modi and Russian President Vladimir Putin began talks in New Delhi on Friday, their second meeting in two weeks, that is expected to focus on trade, energy and defence ties between the two countries, which have long been friends.
UAE President His Highness Sheikh Mohamed bin Zayed Al Nahyan has departed Munich at the end of a multi-day state visit to Germany.
UAE President His Highness Sheikh Mohamed bin Zayed Al Nahyan met with Angela Merkel, former Chancellor of Germany, as part of his state visit to the country.
His Highness Sheikh Khaled bin Mohamed bin Zayed Al Nahyan, Crown Prince of Abu Dhabi, has arrived in India for the 18th BRICS Summit, taking place in New Delhi from September 12 to 13.
