Madrid - The Operation Puerto investigation into the biggest doping scandal in professional cycling has been reopened by Spanish judicial authorities, it was reported Saturday.

El Pais daily said a court in Madrid has overturned a ruling last year by investigative judge Antonio Serrano to close the case.

The ruling could pave the way for criminal proceedings in the investigation.

Operation Puerto was launched after raids in May 2006 in which police found large quantities of anabolic steroids, equipment used for blood transfusions and more than 200 bags of blood linked to more than 50 cyclists.

Serrano had initially closed the case after ruling that there was a lack of evidence that any offences had been committed under Spanish law at the time.

Spain's new anti-doping laws could not be applied retroactively to May 2006, he ruled.

However the case was reopened in February after prosecutors had asked an appeals court to review the decision, only to be closed for a second time. (dpa)