The International Olympic Committee said on Saturday it was still trying to locate Hungarian Olympic hammer champion Adrian Annus, who is suspected of having tampered with his Athens Games doping sample.

Annus, who won gold on Sunday, did provide a negative test after the competition, but the IOC has warned that unless he does a second test he will be stripped of his medal.

"We have reasons to look for him, we have suspicions," IOC spokeswoman Giselle Davies said. She did not say what had gone wrong during the first testing.

Annus returned home after the competition and announced his retirement. But IOC medical supervisors, dispatched to Hungary to locate him, were unable to find and test him.

"Yes, there is ongoing work in this area but at this stage I cannot go into further detail," Davies said.

Annus, 31, shared a coach with Hungary's discus gold medallist Robert Fazekas, who was expelled from the Games after refusing to provide a complete urine sample following Monday's final. Fazekas had to return his medal.

The Hungarian Olympic Committee has backed Annus saying even if he tested positive now, it could have been due to something taken after the Games.