Olympic legend Sebastian Coe organised the 2012 London Games

Lord Coe has described allegations of widespread doping in athletics as a "declaration of war" and says it is time to "come out fighting" to protect the sport's reputation.

The Sunday Times published data from 5,000 athletes, which it says reveals an "extraordinary extent of cheating".

Athletics' world governing body, the IAAF, said the blood results were not positive tests or proof of doping.

"The fightback has to start here," said Coe, an IAAF vice-president.

"It is a declaration of war on my sport. There is nothing in our history of competence and integrity in drug testing that warrants this kind of attack."

What exactly are the allegations?

The Sunday Times and German broadcaster ARD/WDR examined leaked data from the IAAF database of results of 12,000 blood tests between 2001 and 2012.

The reports by the British and German media outlets said that more than 800 athletes - and a third of all medallists in endurance events at recent Olympics and World Championships - had suspicious blood-test results and that they were not followed up by the IAAF.

To review the data, the Sunday Times and ARD/WDR used two of the world's "foremost anti-doping experts", scientists Robin Parisotto and Michael Ashenden, and they said that while "abnormal" results were not proof of doping, they were suspicious.

What is blood doping? Sports nutritionist Eleanor Jones says blood doping can help endurance athletes by increasing their ability to transport oxygen around the body. She told BBC Radio 5 live: "It works like giving blood, except that after you've replaced that donation naturally in your body, you then reinfuse the blood that you removed originally, so you might have 110% of your normal blood volume."

What was the IAAF's response?

In a statement released on Tuesday, the IAAF called the allegations "sensationalist and confusing".

It said: "What the IAAF cannot accept under any circumstances from the ARD/Sunday Times, or the scientists whom they have retained, is an accusation that it has breached its primary duty to act in the best interests of the sport of athletics."

The IAAF called the allegations "guesswork" and said it "categorically refutes all allegations", and specifically rejected the claim that it "failed in its duty to pursue an effective blood-testing programme at all times".

The IAAF says it conducts approximately 3,500 in- and-out-of-competition anti-doping tests every year

We are not sitting on our hands - Coe

Speaking to BBC Radio 4 on Wednesday, Lord Coe backed the IAAF's stance, saying he and the governing body were angered by accusations that they had done nothing to tackle doping.

Coe cited the introduction of the Athlete Biological Passport programme in 2009 as one of the ways the IAAF has been at the forefront of attempts to eradicate doping in sport.

What is the Athlete Biological Passport? An Athlete Biological Passport is an electronic document about the athlete that contains certain biomarkers from through his career. If these markers change dramatically it alerts officials that the athlete might be doping.

"Every athlete in 2012-13 was subjected to a blood test, which was unprecedented. We have led the way on this and have consistently done so," said Coe - who won Olympic gold in the 1500m at the 1980 and 1984 Games and wants to be the next IAAF president.

"To be selectively suggesting that an elevated one-off reading is the same as a positive test is just so wide of the mark. The blood passport itself is designed to create a profile and it is that profile that has chased some of the highest-named athletes out of our sport.

"It has caused intense embarrassment but we have always taken the view that we would rather have short-term embarrassment and protect the clean athletes.

"This is what it is about and that is why we are so angry at the moment."

Sergey Bubka, Coe's rival for the position of IAAF president, says even more transparency in the organisation is needed to aid the fight against doping.

The former Ukrainian pole vaulter also believes a "faster and more efficient" anti-doping system is necessary to ensure the organisation stays "a step ahead of the dopers".

"This is a battle we can't afford to lose, for the sake of athletics and all sports," he said.

"We must be more proactive and even more transparent in our aggressive pursuit of a zero tolerance policy against doping cheats."

BBC Sport's Richard Conway After reports of widespread doping and questions over the validity of 146 Olympic and World Championship medals, athletics is fighting back. Lord Coe believes this is a seminal moment for the sport and in making this intervention, believes that information has been selectively used in this case.

The Sunday Times has its say

The Sunday Times then issued its own statement on Wednesday standing by its story and accusing the IAAF of being "disingenuous" by dismissing their story as sensationalist after spending "just two days conducting what it describes as a 'thorough' investigation".

It also questioned the governing body's level of commitment, adding: "It only employs 10 people to oversee a testing regime covering thousands of athletes across more than 200 countries.

"Its refusal to accept any criticism raises serious questions as to whether the IAAF is truly committed to its primary duty of policing its sport and protecting clean athletes."

The two experts used by the Sunday Times said they "rebutted each and every one" of the IAAF's "serious reservations", saying their judgements were based on the "entire blood-test profile for the athlete not just on individual scores".