British scientists have cast doubts on research purporting to show that an American baby infected with HIV managed to clear the virus from its bloodstream.

Nine Aids scientists from six research centres have written to the journal Nature saying the claim made last March by US researchers was ``premature''.

The American team said that a five-year-old boy born to an HIV-positive mother had tested positive for the virus on two occasions soon after birth but after 12 months he became negative and remained so since.

The announcement caused a stir because it appeared to show it is possible for the body's natural immune defences to fight off what until then had been considered to be a lifetime infection.

However, British researchers, led by Myra McClure of the St Mary's Hospital Medical School in London, say that under the stringent criteria used in the United Kingdom for assessing whether babies are HIV-positive the US baby would not in fact be classified as being infected.