Greece's defending Olympic women's 400 metres hurdles champion Fani Halkia has failed a drugs test, two Greek Olympic Committee officials said on Sunday hours before she was due to start competing in Beijing.

"Halkia tested positive for drugs," one official told Reuters on condition of anonymity, confirming one of the biggest doping cases since the start of the August 8-24 Olympics.

The test was taken around August 10 when Halkiae was in Japan with the rest of Greece's track and field team to prepare for the Games, he said, without giving further details. Athletics at the Games began only on Friday, a week after the opening ceremony.

Halkia denied she had taken performance enhancing drugs.

"I can't believe it ... The first thing I thought of doing was to give all the nutritional supplements I have consumed, my vitamins, for testing," Halkia told Greek reporters in Beijing.

The 29-year-old Halkia was a surprise winner in the 400 metres hurdles at the 2004 Athens Olympics but has rarely raced since then.

The first round of the women's 400 metres hurdles is scheduled for Sunday evening, with the final on Aug 20.

The Greek Olympic Committee said in a brief statement an athlete had been suspended after a first sample had tested positive.

It did not name the athlete but said the person had left the Olympic Village pending the results of tests on a second sample.

REPUTATION DAMAGED

The reputation of Greek sport was seriously damaged on the eve of the Athens Olympics when two medals hopes, sprinters Costas Kenteris and Katerina Thanou, missed a drugs test and withdrew amid a whirlwind of negative publicity.

Thanou, a 100 metres silver medallist in Sydney in 2000, had been barred from competing in Beijing because of her involvement in the Athens doping scandal, the International Olympic Committee (IOC) said a week ago.

A long list of Greek athletes have failed tests over the past few months, including 11 weightlifters, a swimmer and a rower.

One of them, sprinter Tassos Gousis, was sent home from the training camp in Japan after he failed a Greek doping agency test days before he was due to compete.

If Halkia's second sample is positive, the IOC will call an executive board meeting before announcing any action that could include her being banned from the Games and facing more sanctions through the International Association of Athletics Federations.