Rio de Janeiro police rescued three girls as young as 15 among eight people forced to work in a prostitution ring near the beaches where Olympic events will be held. The operation is part of a wider crackdown on sex-trafficking operations ahead of the Games to battle child prostitution.

Child sex tourism is a huge problem along the north-eastern beaches of Brazil, but increasingly more now as the Olympics promises a major influx of foreign visitors, reports AP.

Brazilian prostitutes are reportedly already offering steep discounts on their services to Olympic athletes, journalists, athletic support staff, sports fans, and the usual spate of sex tourists.

A flyer being distributed in Rio — printed in English and featuring the Olympics' five-ring logo — is inviting athletes to take advantage of "early bird" specials. Villa Mimosa, a notorious red light district in Rio, is located not far from the Olympic Village where many athletes will be staying.

The particularly dark side of the trade involves thousands of children forced into sexual slavery as demand increases. Despite more than a decade of government pledges to eradicate child prostitution, the number of child sex workers in Brazil stood at about half a million in 2012. That's a five-fold increase since 2001, when 100,000 children worked in the sex trade, according to estimates by Unicef.

The last major boost in sex tourism for children occurred during the 2014 World Cup when young girls were sold for as little as $2. Sport events are believed to boost demand for young sex workers by as much as 40%, according to experts.

The Justice Ministry of Brazil has been targeting sex tourism, and blocked 2,165 websites operating in different countries between 2012 and 2014. But the number of sites still in operation far exceeds those blocked.