Spanish Vuelta organizers withdrew an invitation to cycling's Team Astana on Monday following three recent doping tests.

"We want to be sure ahead of this edition that we have the cleanest race possible," said Victor Cordero, director of Unipublic, which runs the Vuelta. "We have to protect the purity of the competition as much as we can."

Absent from the September race in Madrid will be defending champion Alexandre Vinokourov, who tested positive for a blood transfusion after winning the 13th stage of the recent Tour de France.

Astana subsequently fired Vinokourov after his "B" sample confirmed the positive result.

Andrej Kashechkin, who finished third in the 2006 Vuelta, also tested positive for homologous blood doping in an unannounced control in Belek, Turkey, on Aug. 1.

On April 24, Matthias Kessler tested positive for abnormally elevated levels of testosterone in a surprise test in Charleroi, Belgium. He was suspended from the team before the July 7 start of the Tour de France.

Astana suspended its activities immediately after Vinokourov's disclosure, with none of its riders competing in any ProTour events in August.

Though Vuelta organizers applauded Astana's decision to suspend the two riders and subsequent attempts to clarify these "deplorable" events, "the urgency of the dates do not allow us to push this decision back any further."

"The Astana Cycling Team's management deeply regrets this decision but respects it," Astana said in a statement. "Consequently, the training camp which had begun last Saturday in the Vallee de Conches, Switzerland, is cancelled with immediate effect."

International Cycling Union president Pat McQuaid said he understood the organizers' decision.

"The whole Astana thing needs to be dealt with," McQuaid said. "I can understand Vuelta organizers not wanting the team in the race."

The three-week tour through Spain, the season's most important race after the Tour de France and the Giro d'Italia, begins in Vigo on Sept. 1.

With files from the Associated Press