PARIS — Several Tour de France riders are having their blood samples retested for traces of the banned blood-booster EPO.

The head of the French Anti-Doping Agency told The Associated Press on Wednesday that the testing involved riders who were already under scrutiny for suspicious urine samples. Pierre Bordry declined to name the cyclists.

The new blood tests will look for CERA, a third-generation variation of EPO. Italian rider Riccardo Ricco tested positive for the substance during the Tour.

"I have decided that we will retest — with blood testing — all those who showed up as suspicious during the urine samples," Bordry said by telephone. "When we did the urine samples of those athletes, we had a serious suspicion that there was CERA. The laboratory could not say definitively. The same analysis will be done, but in the blood samples."

Bordry asked for the blood samples to be sent from Lausanne, Switzerland, where they were tested during the Tour.

"All the blood tests have been repatriated to France," Bordry said, adding that they are currently being examined at the Chatenay-Malabry laboratory, outside Paris.

Testing has already begun and could take up to two weeks, Bordry said.

Calls to Tour director Christian Prudhomme were not immediately returned.

Bordry also said that Spanish rider Moises Duenas Nevado's "B" sample came back positive for EPO, confirming the original finding.

Also testing positive during the Tour were Manuel Beltran of Spain, for EPO, and Dmitriy Fofonov of Kazakhstan, for a banned stimulant.

Ricco and his teammate Leonardo Piepoli were fired by the Saunier Duval team — which also lost its sponsor.

Even though Piepoli did not test positive, he was released for violation of the team's ethical code. Spanish media later reported that Piepoli had admitted to his team that he took the same form of EPO as Ricco.

French cyclist Jimmy Casper tested positive for a banned steroid, but has since been cleared on grounds that he forgot to renew a prescription for a long-standing asthma problem.