The official spoke on condition of anonymity because no official announcement had been made.
Doping expert Michel Audran, of the University of Montpellier in southern France, said he was stunned a rider would resort to a blood transfusion -- a technique that has been detectable since 2004. That was when US rider Tyler Hamilton was caught and suspended for two years.
Blood transfusions work by increasing an athlete's count of red blood cells, which carry oxygen to the muscles.
"Performance can increase between 5 and 20 percent," depending on how much is injected, Audran said.
Condemnation of Vinokourov was particularly vehement from French teams, whose riders have struggled in this and previous Tours against competitors they have long suspected of doping. French teams and laws are more rigorous than most when it comes to fighting doping.
"It's pitiful," Roger Legeay of the Credit Agricole squad, said of Vinokourov's case.
"It's proof that the fight against doping is working. ... There's no pity, even for the big names, and that is great," he told RTL radio.
British rider David Millar, who came back from a two-year doping ban himself and now lobbies for a clean sport, said: "With a guy of his stature and class, in cycling's current situation, we might as well pack our bags and go home."
Around 30 police officers, some in plain clothes, descended on Astana's La Palmeraie hotel in Pau and sealed it off, preventing more members of the team from leaving.
Explosion follows ETA threat
At least one small explosion hit the Spanish section of Wednesday's Tour de France cycle race after a report of a bomb threat from a caller claiming to represent Basque separatist rebels ETA, the government said.
No one was hurt and the Tour, the most important race on the cycling calendar, continued after the explosion.
The caller told a highway authority that ETA had planted several bombs along the route of the Tour de France through the Spanish region of Navarre, newspaper El Pais and other media said.
"At least one device, of little power, has exploded in Belagua, Navarre," a Spanish Interior Ministry spokesman said. El Pais said two bombs had gone off.
The race had already passed through the small town of Belagua at the time of the incident, local media reported.
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