LONDON (AFP) - Failed drug tests by high-profile Jamaican athletes could represent "the tip of the iceberg", according to a leading anti-doping official from the country.

Former men's world record-holder Asafa Powell and women's Olympic relay gold-medallist Sherone Simpson are among the sprinters who have failed tests in recent months.

Dr Paul Wright, a senior official with the Jamaican Anti-Doping Commission (Jadco), says he fears that a recent visit to Jamaica by the World Anti-Doping Agency (Wada) will reveal that doping practices have become widespread.

"The results are not good. This year alone the results really point the finger," he told the BBC. "Remember, all of these results except one were caught by Jadco. The problem is these people were tested positive in competition.

"What that means is months before, you know the date of the test and the approximate time of the test. This could be the tip of the iceberg to have so many positives coming in competition."

Jamaica's testing procedures are due to be discussed at a Wada executive board meeting in Johannesburg later on Tuesday.

Meanwhile, the outgoing president of Wada, John Fahey said his organisation was concerned that Jamaica had "lost their way".

"We have been aware of difficulties in Jamaica for some time," he added.

"We have gone to them, we've assisted them, we have given them some support. We have indicated they need to make some improvements."