An additional 3,000 troops have been added to Brazil's security contingent for next month's Olympic Games as the government redoubles efforts to ensure public safety.

The new soldiers will guard transport infrastructure such as the international airport, subway stations and roads, the justice ministry said on Wednesday.

They will also be used to aid counter-terror operations.

According to justice minister Raul Jungmann, Rio's armed forces headcount for the Olympics now stands at 21,000.

"If necessary, we will mobilize even more," Jungmann said.

The government says 6,000 soldiers have already been deployed in Rio.

During the August 5-21 Games period there will be 12 naval vessels, 28 army helicopters and 70 armed tanks stationed across the city.

Another 20,000 troops will patrol five cities that will co-host Olympic football: Belo Horizonte, Brasilia, Manaus, Salvador and Sao Paulo.

Rio's overall security personnel for the Olympics will be 88,000, including 47,000 police and 41,000 soldiers from the armed forces. The figure is more than double that used for the London 2012 Olympics.