The International Olympic Committee (IOC) has discovered seven more positive drugs results from re-testing samples taken at last year's Beijing Games, stemming from six athletes, it said on Tuesday.
All of them tested positive for CERA (Continuous Erythropoiesis Receptor Activator), the new generation of banned blood-booster erythropoietin (EPO) during the Beijing Olympics last August.
"Of 948 samples that were analysed, seven resulted in an adverse analytical finding (AAF) concerning six athletes," the IOC said in a statement.
The latest round of testing, which began in January, focused primarily on endurance events in cycling, rowing, swimming and athletics, the IOC said.
An IOC official said the samples that had turned out positive were all A samples.
"These were A samples. Athletes in question can now request to be present at the opening of their B samples," an IOC official said.
The official said the IOC would not provide any more details on the individual athletes in question.
The IOC stores samples for eight years to allow re-testing once new methods of detecting banned substances are developed.
"The testing took advantage of improved technology to seek evidence of the prohibited use of CERA [equivalent to the intake of EPO] and insulin," the IOC said.
It said it would not comment on any of the individual cases but had begun the process of notifying the athletes through their national Olympic committees.
Italy's Olympic Committee (CONI) said on its website it had been informed that an Italian competitor was among those concerned but gave no other details.
"The further analysis of the Beijing samples that we conducted should send a clear message that cheats can never assume that they have avoided detection," said Arne Ljungqvist, IOC medical commission chief.
"The vast majority of athletes do not seek an unfair advantage. We intend to do all we can to ensure that they have a fair environment for competition," he said in the statement.
Nine athletes tested positive during the Beijing Olympics after extensive pre-Games testing nabbed about 40 for drugs while six horses in the equestrian events were also found to have been given banned substances.
The IOC conducted the largest ever doping operation with about 5,000 blood and urine tests during the Games.