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.
At least 111 killed after powerful earthquake hits western Colombia
At least 111 people were killed after a powerful earthquake struck western Colombia early on Monday, knocking down buildings across several cities and injuring 87 more, with still others trapped in the rubble.
Storms from Dolphin soak China's east, ground nearly 950 Shanghai flights
Torrential rain and storms in Typhoon Dolphin's wake inundated several provinces in China's east, drenching the coastal region and flooding streets in Shanghai, where around 40 per cent of flights were grounded on Monday due to the weather.
Indian police fire tear gas, use batons to disperse youth protesters
Police in eastern India used tear gas, batons and water cannon to disperse thousands of youth protesters as they marched on the state legislature in Jharkhand state on Monday over alleged wrongdoing in civil service examinations.
China says Long March 7A rocket launch failed after flight anomaly
China said a Long March 7A rocket carrying the ChinaSat-4B satellite failed after an in-flight anomaly following liftoff from the Wenchang space launch site in the southern island province of Hainan on Monday.
Ukraine kills 13 in drone strikes on Russian city of Nizhnekamsk, officials say
At least 13 people were killed and 39 injured in a Ukrainian drone attack on industrial and civilian targets in the city of Nizhnekamsk, authorities said on Monday, one of the heaviest civilian tolls in Russia in months.
