Members of a huge police force sent to secure crime-ridden Rio before the Olympics next month have already come under gunfire, officials said as Brazil's interim president promised "absolute peace" at the Games. The shooting incident in the troubled north of Rio de Janeiro underlined the challenge to ensuring safety for the 10,500 athletes and 500,000 tourists expected at the August 5-21 Olympics, the first ever to be held in South America. Brazil is deploying some 85,000 police and soldiers, double the number used for the London 2012 Olympics, with the vast majority in Rio and others in cities where the football matches are set to take place. The attack on an elite police unit on Tuesday was the first since the reinforcements started to deploy, although similar shootings between city police and drug traffickers take place almost daily. "A vehicle from the national force was returning from a reconnaissance mission when it was shot at," a spokesman for the Justice Ministry told AFP. "A wing mirror was hit, but no one was injured. The agents returned fire and exchanged shots in an exchange that lasted a few seconds." O Dia and Globo newspapers reported the incident, which comes against a backdrop of soaring muggings and a rise in murders over the last year. However, officials on Wednesday said visitors to the Olympics have nothing to fear. "The country has put together a solid security program. to ensure that sporting events take place in an atmosphere of absolute peace and tranquility," Brazil's interim president Michel Temer said. "This contingent of security personnel will work in an integrated fashion, overseeing the protection of athletes, coaching staff, heads of state, government officials, local residents and journalists," he added in an open letter posted in English on the Facebook page of the country's Olympic organizing committee. Defense Minister Raul Jungmann told a news conference that he could guarantee "peace, with the happiness and calmness that we expect."