The controversial decision to award the 2021 World Athletics Championships to Eugene, Oregon, is being investigated by the FBI and the Criminal Division of America's Internal Revenue Service (IRS), the BBC has learned.
The US city was awarded the event in 2015 with athletics' governing body the IAAF bypassing the usual formal bidding process.
French prosecutors investigating corruption within the IAAF launched their own inquiry into the awarding of the event in 2015.
Former IAAF president Lamine Diack, who is now effectively under house arrest in France over corruption allegations, was at the centre of the decision.
Eugene was handed the event despite strong interest from the Swedish city of Gothenburg.
The Oregon city is closely associated with Nike, whose birthplace is only a few miles away.
Nike funds much of the University of Oregon's sports facilities, where many of Eugene 2021 events will be held.
A BBC story in November 2015 suggested the IAAF president Lord Coe may have lobbied his predecessor over the bid, and revealed he had discussed it with a senior Nike executive.
At that time Lord Coe was paid £100,000 a year as an ambassador for Nike. Lord Coe denied he had lobbied anyone on behalf of Eugene's bid.
However, he stepped down from his Nike role - which he had held for 38 years - later that month saying accusations of a conflict of interest were "a distraction" and "not good for Nike or the IAAF".
Bjorn Eriksson, who was the head of the Gothenburg team denied the opportunity to stage a rival bid, said it had been a 'violation of fair play.'
Now, the BBC understands, the American authorities - including tax investigators at the IRS - are seeking to investigate if there has been any wrongdoing committed in the US, bringing to total number of agencies investigating the awarding of the championships to three.
A spokeswoman for the IAAF and Lord Coe said she was unaware of any FBI and IRS probes.
"The IAAF team has not received notification from the FBI or IRS. However we are committed to working closely with any key investigation, as we do with the French investigation team, and will take action if proof is found of any wrong doing in an IAAF bidding process."
Both the FBI and IRS have yet to respond to the BBC.
The FBI famously investigated corruption in football's world governing body Fifa, resulting in guilty pleas from numerous high-ranking officials.
The Eugene bid was led by Vin Lananna's TrackTown USA, another organisation with close links to Nike.
The 2015 BBC investigation uncovered emails which claim Coe - an ambassador for sports giant Nike and then vice-president of world athletics - "reached out" to Diack with his support for Eugene's bid.
After of losing out in a bid to host the 2019 championships to Doha, Lananna and TrackTown USA quickly turned their attention to 2021, and began lobbying the IAAF.
Coe had been on the IAAF evaluation commission which visited Doha, Eugene, and the other unsuccessful bidder for 2019, Barcelona.
An email sent by Nike executive Craig Masback to Lananna suggested that Coe lobbied on Eugene's behalf.
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.
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".
Other emails seen by the BBC revealed 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, the campaign had paid off.
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.
The BBC has contacted Lananna and TrackTown USA for a response.