Sebastian Coe was under mounting pressure after a leaked email suggested that he had lobbied Lamine Diack, the former IAAF president, to give the world championships to Eugene, Oregon, a city synonymous with Nike.

The BBC said that it had seen an email exchange in which it was claimed that Coe had "reached out" to Diack, now the subject of a corruption inquiry. Since succeeding Diack in August, Coe has been widely condemned for refusing to give up a £100,000-a-year global adviser role with Nike, claiming that there is no conflict of interest.

The IAAF awarded the 2021 world championships to Eugene in April without a formal bidding process. Nike was founded in Eugene and has a museum in its store in the city.

Now an email from January has added to the burden facing Coe, who is awaiting the World Anti-Doping Agency's report into IAAF corruption.

The email from Craig Masback, director of business affairs for Nike's Global Sports Marketing, was sent to Vin Lananna, president of Track Town USA, the bid organiser. It said: "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.'"

Diack reportedly changed his mind at that IAAF council meeting in April. An IAAF council member told the BBC: "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." The vote to forgo a formal bidding process and hand the world championships to Eugene was carried 23-1 on April 16.

Gothenburg had been encouraged to launch a 2021 bid. Bjorn Eriksson, its bid leader, said: "It smells and has to be investigated."

Coe said he had told Swedish Athletics that there would be a formal bidding race as that was his belief until the Beijing meeting.

Diack had assured him that was the case, so he encouraged Eugene and Gothenburg to bid.

Coe denied that he had lobbied Diack, but felt that Eugene had a strong bid after narrowly losing out to Doha for 2019. Coe said: "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."

Coe said on Tuesday: "The overwhelming majority of IAAF council members decided to take the championships into a market where we have never been before. The situation was unusual, but not unprecedented."

Osaka was given the 2007 world championships without a race. Coe said that the bidding process was part of his forensic review of IAAF methods.