Hundreds of police troops took up position in two volatile Rio de Janiero favelas, part of a drive to clean up the city for the June-July World Cup and the 2016 Olympics.
The favelas in Rio's north, Complexo do Alemao and Penha, are among those authorities say they have "pacified," but a renewed uptick in organised crime and violence in recent weeks has regularly targeted police and security forces.
A policeman was shot dead in clashes with drug traffickers in another "pacified" shantytown in Rio on Thursday, while another was killed yesterday in another area.
Rio Governor Sergio Cabral said that he was in "no doubt it is an orchestrated action by criminals to kill police officers."
Four hundred police officers, among them special forces decked out in black, "formed a security cordon" in Complexo do Alemao and Penha, said Colonel Frederico Caldas.
"Our response will be extremely forceful," he warned.
Rio will host seven World Cup matches, including the final.
