The International Association of Athletics Federations says it will not rule out "any follow-up action necessary" over a Sunday Times report alleging widespread doping in the sport.

The newspaper, and German broadcaster ARD/WDR, obtained leaked data relating to 12,000 blood tests conducted on more than 5,000 athletes.

Experts enlisted by the Sunday Times claimed the data showed that more than a third of medals - including 55 golds - awarded at Olympic Games and World Championships between 2001 and 2012 were won by athletes with suspicious tests.

It was further alleged that none of those medals had been taken away by the authorities.

The IAAF appeared angered that the data had been published at all and said it would now be contacting both media outlets for more information.

"The IAAF is aware of serious allegations made against the integrity and competence of its anti-doping programme," a statement from the organisation read.

"The relevant allegations were broadcast in Germany yesterday and have been repeated in an article in the Sunday Times newspaper today.

"They are largely based on analysis of an IAAF database of private and confidential medical data which has been obtained without consent. The IAAF is now preparing a detailed response to both media outlets and will reserve the right to take any follow up action necessary to protect the rights of the IAAF and its athletes."

The World Anti-Doping Agency said it was "very alarmed" by the Sunday Times report.

WADA president Craig Reedie said: "WADA is very disturbed by these new allegations that have been raised; which will, once again, shake the foundation of clean athletes worldwide."

"So many athletes appear to have doped with impunity, and it is damning that the IAAF appears to have idly sat by and let this happen" - Scientist Robin Parisotto

He also announced that given the nature of the allegations, they would be handed over immediately to the organisation's independent commission for further investigation.

Reedie said: "These allegations require swift and close scrutiny to determine whether there have in fact been breaches under the World Anti-Doping Code and, if so, what actions are required to be taken by WADA and/or other bodies.

"As always, WADA is committed to doing what's necessary to ensure a level playing field for clean athletes of the world."

It is also alleged that a top UK athlete is among seven Britons with "suspicious" blood scores, while it is claimed that 10 medals were won at the London 2012 Olympics by athletes who had reportedly recorded dubious test results.

Among the other claims, the Sunday Times says more than 800 athletes - one in seven of those named in the files - have recorded blood-test results described by one of the experts as "highly suggestive of doping or at the very least abnormal", and that more than a third of the world's fastest times in endurance events were recorded by athletes whose tests have triggered suspicion.

Scientist Robin Parisotto said: "Never have I seen such an alarmingly abnormal set of blood values...So many athletes appear to have doped with impunity, and it is damning that the IAAF appears to have idly sat by and let this happen."

Exercise physiologist Michael Ashenden was also critical of the IAAF in the Sunday Times, saying: "For the IAAF to have harvested millions of dollars from the broadcasting of athletics events around the world...yet only devote a relative pittance of those funds towards anti-doping, when they could see the terrible truth of what lay beneath the surface, is... a shameful betrayal of their primary duty to police their sport and to protect clean athletes."

The Sunday Times reported that the IAAF had threatened to take out an injunction preventing the newspaper from publishing details of the files before it dropped its action on Friday.