Alexandre Vinokourov of Kazakhstan reacts as he crosses the finish line to win the 15th stage of the 94th Tour de France on Monday. ((Associated Press))

Team Astana pulled out of the 94th Tour de France on Tuesday after one of its riders, Alexandre Vinokourov, tested positive for a banned blood transfusion.

The positive test of the Kazakh rider, a one-time favourite to win cycling's premier event, dealt a heavy blow to a sport already reeling from a spate of doping scandals.

"Vino has tested positive having to do with a blood transfusion and the team is leaving the Tour," team spokeswoman Corinne Druey said, usingVinokourov's nickname.

Tour de France organizers said the race would go on.

French daily newspaper L'Equipe reported on its website that the positive test occurred after Vinokourov's victory in the 13th-stage time trial on Saturday.

The story addedthatanalysis, conducted by the Chatenay-Malabry lab on the outskirts of Paris, revealed two distinctive types of red blood cells found in the A sample, and showed that Vinokourov received a blood transfusion from a compatible donor shortly before the time trial.

Pat McQuaid, president of cycling's world governing body, the UCI, said he could not comment as long as the result of the backup B-sample had not been confirmed.

"We have a process in place and we have to see this process through," McQuaid said.

A pre-race favourite, Vinokourov won two stages this year— the time trial in Albi and Monday's 15th stage— and stood 23rd in the overall standings.

Hedropped out of contention for good Sunday after losing 28 minutes, 50 seconds to race leader Michael Rasmussen.

The Tour finishes in Paris on Sunday and race director Christian Prudhomme said the case showed that cycling's drug-testing system doesn't work.

"It's an absolute failure of the system," he said. "It is a system which does not defend the biggest race in the world. This is a system which can't last."

World Anti-Doping Agency chief Dick Pound, a frequent critic of cycling's doping record, said the sport should have cleaned itself up by now.

"It's almost impossible to be at the front of the pack these days without doping," the Montreal lawyer said.

Vinokourov was injured in a crash in the fifth stage, requiring stitches in both knees.

"With a guy of his stature and class, in cycling's current situation, we might as well pack our bags and go home," said British rider David Millar, who came back from a two-year doping ban in the Tour last year.

Tour de France officials expressed dismay at the latest doping case to scar the event and the sport as a whole.

"Everyone will feel betrayed," said Patrice Clerc, head of Amaury Sports Organization, which owns the Tour. "The public wants to see a credible winner."

But Clerc said it "never crossed my mind" to halt the Tour.

"We have started a war against doping," he said. "It's out of the question to give up."

With files from the Associated Press