IAAF president Lord Coe is facing conflict of interest allegations after an email emerged suggesting he lobbied his predecessor over the hosting of the 2021 World Championships.
Eugene, USA, was given the event without a bidding process, despite interest from the Swedish city of Gothenburg.
A BBC investigation has uncovered emails which claim Coe - an ambassador for sports giant Nike and then vice-president of world athletics - "reached out" to Lamine Diack with his support for Eugene's bid.
The Oregon city, which lost out to Doha with a 2019 bid, is closely associated with Nike.
Leader of the Gothenburg bid at the time and former head of Interpol, Bjorn Eriksson, told the BBC that the conflict of interest allegations needed "an explanation".
When asked about the allegations, Coe told the BBC he "did not lobby anyone" over Eugene's bid, but "encouraged them to re-enter another bidding cycle as they had a strong bid".
The British former Olympic 1500m champion was elected as president of athletics' governing body in August. He received £63,000 from UK Sport to pay for his PR team as part of the election process and said the rest of his campaign was "privately funded".
Coe says that all of his interests were declared to the IAAF's ethics committee and that his views on all the bids for the 2019 World Athletics Championships and Eugene's 2021 bid "are all a matter of public record".
Senagalese Diack, 82, is being investigated over allegations he took payments for deferring sanctions against Russian drugs cheats.
After the World Anti-Doping Agency's (Wada) independent commission report recommended Russia's athletics federation be suspended from international competition, Coe said track and field faced a "long way back" from a "shameful situation" - but that he was "more determined than ever" to lead the sport.
The report's co-author Dick Pound will be publishing the second part of his report later this year, focusing on alleged IAAF corruption.
How was the 2021 decision made?
Coe had been on the IAAF evaluation commission which visited Doha, Eugene, and the other unsuccessful bidder for 2019, Barcelona.
After its disappointment, Track Town USA, the organisation behind the Eugene bid - which is closely associated with Nike - quickly turned its attention to 2021, and began lobbying the IAAF.
The efforts of Vin Lananna, Track Town USA's chief, paid off and in April this year at an IAAF meeting in Beijing, Diack announced a surprise vote on whether to bypass a normal bidding process, and simply hand the 2021 games to Eugene.
Several IAAF council members have told the BBC that Diack made clear his support for Eugene, and urged his fellow members to follow suit. The secret vote was carried by 23-1, with one abstention.
A bid process did not take place when the Japanese city of Osaka was awarded the 2007 World Championships.
What was the reaction?
Eriksson, the then head of Swedish athletics who was in charge of Gothenburg's bid, told the BBC he had been personally assured by both Coe and Diack that it would get a chance to bid for 2021.
"The idea we don't even get the chance to deliver an offer, we don't get the chance to be judged," he said. "That makes me still furious."
Eriksson is now demanding answers over whether Coe himself played any role in the process.
Coe told the BBC he believed the 2021 games would only be awarded after a bidding process until the IAAF council meeting in April, at which Diack told its members to award the event to Eugene.
Lananna is on record as saying that neither Nike nor Coe had anything to do with the bidding process, other than Coe's right to vote on it as an IAAF member.
So what was in the email?
The BBC has obtained an internal Nike email that could throw doubt on that claim.
The email, dated 30 January 2015, is from Craig Masback, director of business affairs for Nike's Global Sports Marketing, to Lananna and Robert Fasulo, both from Track Town USA.
Masback was chief executive for USA Track and Field (USATF) for more than 10 years before joining Nike in 2008.
The email, titled '2021' and in which Coe is referred to as "Seb", reads: "I spoke with Seb this morning. We covered several topics but I asked specifically about 2021.
"He made clear his support for 2021 in Eugene but made equally clear he had reached out to Diack specifically on this topic and got a clear statement from Diack that 'I am not going to take any action at the April meeting (in Beijing) to choose a 2021 site'."
Yet it was at that April meeting of the IAAF's council that Diack announced the surprise vote on giving the championships directly to Eugene.
|Analysis by BBC sport editor Dan Roan:|
|"This is the last thing athletics needs when it is trying to regain much-needed confidence and trust back from the public just weeks after a damning Wada report which revealed systemic-state sponsored doping in Russia.|
|"That led to the country being banned from international competition and allegations of extortion and cover-ups at the IAAF. Lord Coe is now the man at the helm and it is his job to clean up track and field.|
|"The problem he faces is that many have questioned whether it is right that one of the world's leading sportswear manufacturers, Nike, pays him a reported six-figure sum each year to be a brand ambassador.|
|"Nike sponsors Russia's athletics team (now banned for systemic doping claims), it sponsors two-time drugs cheat US sprinter Justin Gatlin, it employs coach Alberto Salazar, (currently under investigation by USADA for allegedly breaching doping rules), and it stands to gain hugely from the world championships going to its hometown in 2021.|
|"Next week Coe will appear before a parliamentary committee and MPs are almost certain to ask him why he was in discussion with a senior Nike executive over the 2021 games and whether the time has come for him to end that association."|
What happened next?
Other emails seen by the BBC reveal that Lananna made at least one trip to Europe to visit Diack a few weeks after this email was written.
And by 15 April 2015, Track Town USA's campaign had paid off.
"We got 24 hours' notice of this vote and it was made clear to us what Lamine wanted - he wanted Eugene to get these championships," an IAAF council member told the BBC. The decision was announced on 16 April.
'It smells and needs investigating'
The BBC showed the emails to Eriksson, who is also the former president of international police organisation Interpol.
"It doesn't look good. It doesn't good at all. I would very much [like to] hear the explanation for this," Eriksson said. "I've never seen it before.
"I would very much like to hear how could this be explained. It is a very good question to Sebastian Coe. What is this?"
Asked how he felt about the whole 2021 process, Eriksson said: "It smells and it has to be investigated. That's for the sport, for everybody involved."
Eriksson also cautioned Coe on his association with Nike, which is reported to be worth around £100,000 per year to the double Olympic gold medallist.
He said: "I'd say it doesn't help at all, I'd say it's a major problem."
What about Nike's role in this?
While Nike is not an official IAAF sponsor, it could benefit from the games being held in Eugene.
Nike is a global superpower in athletics - particularly in the USA where it has a sponsorship deal with USATF until 2040 - but came in for criticism when it re-signed twice-banned American sprinter Justin Gatlin.
It is also the kit sponsor for the Russian athletics federation - the subject of a recent, damning report by a Wada independent commission.
And earlier this year, the elite Nike Oregon Project training camp and its coach Alberto Salazar was at the centre of doping allegations by BBC Panorama, which have been denied, but remain the subject of a US Anti-Doping Agency investigation.
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Lord Coe's responses to the BBC
Q: Did you lobby the IAAF and/or Lamine Diack on behalf of Eugene 2021? If so, given your role with Nike and Nike's close association with Eugene and Track Town USA, what would you say to those who would consider this to be a conflict of interest?
A: No, I did not lobby anyone on behalf of the Eugene 2021 bid. After their narrow defeat for the 2019 Championships I encouraged them to re-enter another bidding cycle as they had a strong bid. My views on all the bids for the 2019 World Athletics Championships (including Eugene) are a matter of record as I was chair of the evaluation commission for those bids. All my interests were, and continue to be, fully declared to the IAAF ethics committee and listed at the House of Lords.
Q: Did you ever discuss the Eugene 2021 bid with any Nike employee, official or executives? If so, with whom, and when?
A: Not unless I was asked if Eugene should rebid to which I would have replied 'yes' given how close they came to winning and the strength of their bid. My views are all a matter of public record as the media covered this extensively at the time.
Q: Did you tell any Nike employee, official or executive in January 2015, that you were in favour of the IAAF World Championships coming to Eugene in 2021? If so, given your position at the IAAF, what would you say to those who would consider this advance statement of support to be a conflict of interest?
A: I have long believed we should have a World Championship for athletics in the USA given the strength and size of this market and have had discussions with US Track and Field, the USOC (United States Olympic Committee), and cities and states in the USA many times. It is up to those organisations to put forward the proposal of a city, not me.
Q: The BBC has been told by Swedish Athletics that it was assured by you personally, as well as by Lamine Diack, that the 2021 games would only be awarded after a bidding process. Did you say this? If so, how do you then explain what happened?
A: I would have done as that was my view right up to the council meeting in Beijing when president Diack told the council of 25 people there were political and financial considerations in terms of the way the funding package came together for Eugene that may not be present again and we should award 2021 to Eugene. The overwhelming majority of IAAF council members from all parts of the globe decided to take the world track and field championships into a market where we have never been before. The situation was unusual but not unprecedented. A bid process did not take place when Osaka was awarded the 2007 World Championships. The process for bidding is already being reviewed as part of a wide range of reforms currently being prepared.
Q: The BBC understands that a significant amount of public money, via UK Sport, was made available to you to help fund your presidential campaign. In light of the events at the IAAF, which some say stands accused of being "worse than Fifa", do you believe this was good value for money for the UK taxpayer? If so, why?
A: I am very grateful for UK Sport's assistance. It was offered to me, and to others, as part of UK Sport's role to promote the UK's sporting interests internationally by assisting with the appointment of individuals into key international roles. Two thirds of the campaign was privately funded.
Q: UK Sport has confirmed that it provided £63,000 worth of funding to pay for your PR team at Vero. Can you confirm how you funded the rest of the campaign? ie. travel and expenses?
A: Two-thirds of the campaign was privately funded.