SINGAPORE - Two of sport's biggest names will not be in Singapore for the inaugural Youth Olympic Games.

The International Olympic Committee (IOC) told MediaCorp on Friday that swimming superstar Michael Phelps and track phenomenon Usain Bolt (picture) are unable to attend the Games.

Along with Olympic pole vault champion Yelena Isinbayeva, the pair were appointed Games' ambassadors by the IOC for more than 3,600 young athletes from the 205 National Olympic Committees that will compete in Singapore from Aug 14 to 26.

"We just heard from Michael and Usain, and they will not be able to join us in Singapore because of their competition schedules," IOC media relations co-ordinator Nimtaz-Tanya Noordin said.

American Phelps, 25, has 14 Olympic gold medals to his name, the most in the history of the Games. Jamaica's Bolt is the reigning 100m and 200m Olympic champion and world-record holder.

It was hoped the presence of the two biggest stars of the 2008 Beijing Games would help hype up the Youth Olympic Games, but both athletes confirmed they will miss out on their Facebook page.

"Even though I can't make it in person, because I'll be competing at the US Nationals and (hopefully) Pan-Pacific (Championships), I will definitely be there in spirit," wrote Phelps, who won a record eight golds at the 2008 Olympics.

"I wish all the athletes good luck and most of all have fun!"

Bolt, who clinched three golds in Beijing, billed the Youth Olympics as important for the development of young athletes. Said the 23-year-old on his Facebook page: "My advice to the athletes going to Singapore is to first of all have fun. Just remember all the hard training you did, do what you enjoy and you will always succeed."

Without them, Isinbayeva will be the only Games ambassador coming to Singapore. She will be joined by 46 athlete role models selected by the IOC as part of the Games' culture and education Programme.

The group includes four-time Olympic gold medallist and 10-time Chinese women's diving champion Guo Jingjing, Moroccan middle-distance great Hicham El-Guerrouj, Russian swimming legend Alexander Popov and pole vault legend Sergey Bubka of Ukraine.

The Youth Olympics will feature 201 events across 26 sports and feature athletes aged between the ages of 14 and 18.