A police officer and 24 people were killed in a clash that broke out in a Brazilian slum during an operation against illegal groups, according to media reports.
Police carried out an operation in Jacarezinho in northern Rio de Janeiro with 200 officers.
Officer Andre Frias was shot in the head and two dozen suspects were killed.
At least two passengers on a train were injured from bullets that hit the metro.
A gang controlling Jacarezinho town is accused of recruiting children to commit crimes.
According to the online portal, Fogo Cruzado, which tracks armed conflicts in Brazil, it is the highest number of casualties reported since 2016.
The Supreme Court last year suspended police from launching raids in favelas during the coronavirus pandemic but allowed operations in exceptional cases.
*Writing by Faruk Zorlu in Ankara
