French national anti-doping agency (AFLD) chief Pierre Bordry on Wednesday said there was "considerable evidence" of doping irregularities from blood transfusions taken at this year's Tour de France.
"We possess considerable evidence from blood transfusions. We will only say later who it is," Bordry told German TV station ZDF.
He added that anti-doping officials were concentrating on looking for traces of banned blood booster EPO, "but we will soon be able to test the transfusions thanks to a new procedure, and we are going to do these tests.
"Some suspected cyclists returned to normal levels, but it was astonishing to see at what point their performances had then slowed," said Bordry.
Bordry added he had already been in contact with around 30 cyclists who are thought to be embroiled in the latest scandal to hit the Tour de France.
Earlier this week two cyclists tested positive for the difficult-to-detect, new-generation EPO-type blood booster CERA.
Leading German cyclist Stefan Schumacher, a double stage winner, tested positive on Monday while Leonardo Piepoli, who won the 10th stage, has been handed a 20-month ban.
During the Tour only four drugs cheats were snared: Manuel Beltran, of Liquigas, and Barloworld rider Moises Duenas tested positive for EPO.
Italian star Riccardo Ricco then joined them in disgrace after testing positive for CERA, and on the race's final day Dmitri Fofonov, who rides for Credit Agricole, tested positive for a banned stimulant.
© AFP 2008