The 21-year-old Inter Milan player, who is Fifa's world football player of the year, is to help raise awareness among young people of the importance of safer sex, and get them more involved in community initiatives to combat the global epidemic.

Around 10 million of the 30 million people with HIV worldwide are aged between 10 and 24, according to UN figures. And five young people are infected with HIV every minute.

Play safe!

Ronaldo, who is currently training for the World Cup, is depicted on a signed UN poster bearing the message "Play Safe!".

The poster will be used by UNAIDS, a programme grouping together six major UN agencies, in its 'Force for Change: World Aids Campaign for Young People' which was launched last April.

Five young people per minute are infected with HIV

Ronaldo's role will develop after the World Cup. He said: "As a young person, I am very aware of the threat of this virus [HIV], and I believe that I can play an important role in standing up to this threat. It is up to us, the young people of the world, to make a difference."

He added that many young people mistakenly thought they could not get infected if they knew their partner. "We need to protect ourselves and our partners each and every time. When I play to win, I play safe!" he said.

Kindness

Dr Peter Piot, executive director of the UNAIDS programme, welcomed Ronaldo's involvement in the campaign.

He said: "Ronaldo has captured the imagination of young people all over the world.