Allegations that athletics chief Lord Coe lobbied for Eugene to host the 2021 World Championships need an "explanation", according to the leader of Gothenburg's rival bid.
The IAAF president Lord Coe has denied allegations of a conflict of interest over his relationship with Nike and his role in the Oregon city of Eugene being awarded the 2021 championships, following a BBC investigation.
Bjorn Eriksson, leader of Gothenburg's 2021 bid and the former Interpol president, told the BBC: "It smells and needs to be investigated".
Eugene - closely linked to sportswear giant Nike - was awarded the 2021 event without a bidding process, despite strong interest from Swedish city Gothenburg.
"It doesn't look good at all," Eriksson told the BBC on being shown emails which claim Lord Coe contacted then-IAAF president Lamine Diack to support Eugene's bid.
"I would very much like to hear how could this be explained. It is a very good question to Sebastian Coe. What is this?
"It smells and it has to be investigated. That's for the sport, for everybody involved."
Nike ambassador Coe was an IAAF vice president when he is alleged to have championed Eugene's bid.
"I'd say it doesn't help at all, I'd say it's a major problem," said Eriksson, of Coe's association with Oregon-based sportswear brand Nike.
Folkestone and Hythe MP Damian Collins called for Coe to cut all ties with Nike in order to continue with the IAAF.
The House of Commons culture, media and sport select committee member tweeted: "Seb Coe should end his job with Nike if he is to continue as President of the IAAF. The perception of conflicts of interest is too great."
Coe was elected IAAF president in August and has since campaigned against corruption within the sport, which is facing a major doping scandal.
Diack is being investigated over allegations he received payments to defer sanctions against Russian drug cheats.
The BBC investigation centred around an internal Nike email from January claiming Lord Coe gave assurances he supported the Eugene bid, but had been told by Diack that no decision on 2021 championships would be made in April.
Diack later announced the award of the 2021 championships in April, catching many by surprise.
Coe insisted he had not made any attempts at lobbying for the Eugene bid, defending the IAAF awarding the games without an official bidding process.
"I did not lobby anyone on behalf of the Eugene 2021 bid," Coe told the BBC.
"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."
The IAAF issued a statement in response to the BBC investigation, attempting to clarify the sequence of events.
"Much has been written about the unusual but not unprecedented way in which Eugene was awarded the 2021 World Championships," read the IAAF statement.
"Seb believed, along with many other council members, that the usual process would be followed and encouraged Eugene to enter the bidding cycling for 2021 which would be decided in November 2016.
"He sought clarity from President Diack when asked by Gothenburg about the 2021 bidding process and received assurances that no decision would be made at the April Council meeting so he continued to encourage Gothenburg and Eugene to both put themselves forward for the 2021 bidding cycle."