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.
Trump says no rush for Iran deal, US blockade stays
US President Donald Trump said on Sunday he had told his representatives not to rush into any deal with Iran, as his administration played down hopes of an imminent breakthrough in the three-month-old war that had been raised a day earlier.
Iran says ship traffic at Strait of Hormuz will return to pre-war level in 30 days
A potential deal between Iran and the United States stipulates that the number of ships able to transit the Strait of Hormuz would return to the pre-war level within 30 days, according to Iran's semi-official Tasnim news agency.
Netanyahu tells Trump Israel will remain free to act against threats
Israeli Prime Minister Benjamin Netanyahu told US President Donald Trump Israel would remain free to act against threats in Lebanon during a phone call about an emerging agreement between Washington and Iran on Saturday, an Israeli source said.
Turkish riot police enter opposition headquarters to evict ousted leadership
Turkish riot police fired tear gas and forced their way into the main opposition party's headquarters to evict its ousted leadership on Sunday, a Reuters witness said, further inflaming a political crisis.
At least 24 killed after powerful bomb explodes in Pakistan's Quetta
A bomb blast hit a shuttle train carrying Pakistani security personnel and their families in the southwestern province of Balochistan on Sunday, officials said, in the latest major attack claimed by separatist fighters.
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