Thirteen men suspected of planning to rob a bank in Brazil have been shot dead by police.

Three other suspects and a police officer were also injured in the shootout in Salvador.

"A group of 30 men was planning to rob a bank branch," the Bahia state headquarters of the military police said.

Police reportedly arrived as the would-be robbers were setting up explosives next to the cash machine.

Salvador is the capital of Bahia, the fourth most populous state in Brazil with just over 14 million residents.

Bahia public security secretary Mauricio Barbosa defended Friday's operation.

"The police must act with severity, they must be tough. They can't do it arbitrarily, of course, but they must act firmly," he said. 

But rights activist Rafael Custodio said Brazilian police have a "war mentality".

"The police are applauded for bringing in bodies," the lawyer with rights group Conecta said.

(Sky News)