Sex tests carried out on Caster Semenya, the world 800 metres champion, show that she is a hermaphrodite, a source close to the case claimed last night.

If the allegation is backed up by the official results, the South African may find herself stripped of her gold medal and banned from racing. The IAAF, the world governing body, refused to comment on the claim last night, but earlier in the day its general secretary, Pierre Weiss, said: “It is clear that she is a woman but maybe not 100 per cent.”

Semenya was believed to have gone into hiding last night and it is understood she is unlikely to appear in her first race since winning the gold last month. Her coach, Michael Seme, said he was now uncertain whether Semenya would compete at the 4,000 metres women’s event at the South African national cross-country championships in Pretoria tomorrow.

Leonard Chuene, the president of Athletics South Africa (ASA), which has been vocal in its criticism of the IAAF, said: “We cannot get involved in gossip of this sort. Our people will speak to Caster and ensure that she puts these rumours from her mind.”

They are unlikely to be successful. The source, who is said to be close to the IAAF investigation, claimed that the 18-year-old athlete had internal testes and no womb or ovaries.

The situation is extremely delicate because of a lack of precedents and Semenya’s high profile in South Africa. The African National Congress Youth League has already accused the IAAF of racism, while Mr Chuene has resigned from the IAAF Council in protest. The source told the Australian Daily Telegraph: “There certainly is evidence Semenya is a hermaphrodite, but the trouble is the IAAF now have the whole ANC and the whole of South Africa on their backs.”

The ill feeling between the IAAF and ASA has been festering since the story broke on the day of Semenya’s final three weeks ago.

The IAAF claim gender verification tests were done in South Africa when their attention was drawn to her huge improvement at the Africa Junior Championships in Mauritius in July. ASA denies that these tests took place and says that the only tests were done by the IAAF during the World Championships in Berlin.

However, it is known that the pre-Berlin tests revealed high levels of testosterone. Nick Davies, IAAF spokesman, said: “If she has excessive testosterone levels that can be treated, then she needs to consent to do this.”

The IAAF is still lacking the South African tests, which it wants to back up its own findings. At yesterday’s press conference at the World Athletics Final in Salonika, Greece, Mr Weiss said: “We have to see if she has any advantage from her possibly being between two sexes.”

Last week Wilfred Daniels, a top South African athletics coach, resigned after accusing the country’s athletics chiefs of duping Semenya into taking sex tests in Pretoria before the World Championships. Semenya was led to believe that they were routine drug tests. ASA denies that the tests were carried out.

The IAAF’s policy document on gender verification states that if there is any suspicion, an athlete can be asked to go before a panel including a gynaecologist, psychologist and an expert on transgender issues. In 2006 an Indian 800 metres runner, Santhi Soundarajan, was stripped of her silver medal at the Asian Games after “failing” a sex test. She was later found to have AIS and was reported to have made a suicide attempt.

Semenya’s mother Dorcus Semenya said last night: “Why must jealousy drive people to say such bad things? They are crazy. It must be jealousy that makes them say she is a man.”

Hermaphroditism

— A hermaphrodite is an organism that has both male and female reproductive organs

— The term comes from the name of the minor Greek god Hermaphroditus, son of Hermes and Aphrodite, who was fused with a nymph, Salmacis, resulting in one individual possessing physical traits of both sexes

— The great majority of pulmonate and opisthobranch snails and slugs are hermaphrodites

— Hermaphroditism is also found in some fish and in some other vertebrates

— "Hermaphrodite" is used in botany to describe a flower that has both staminate (male, pollen-producing) and carpellate (female, ovule-producing) parts. This condition is seen in many common garden plants

— The mythological figure of Tiresias, who figures in the Oedipus cycle as well as the Odyssey, could be called a sequential hermaphrodite, having been changed from a man to a woman and back by the gods