GENEVA -- FIFA's reputation depends on resolving allegations about Qatar's selection as the 2022 World Cup host, according to the governing body's anti-corruption advisers.

The expert panel chaired by Swiss law professor Mark Pieth gave its full support on Wednesday to a FIFA investigation of the 2018 and 2022 World Cup votes, led by ethics prosecutor Michael Garcia.

"The ethics committee should not rest until there is a conclusive answer," Pieth wrote in a report to FIFA board members, some of whom agitated last month to remove Garcia from the case.

"If FIFA is to emerge from the scandals of recent years it must now produce a convincing and transparent answer to any issues relating to hosting decisions, either to confirm that the suspicions are, sadly, well founded or to demonstrate that they are groundless," the report said.

The comments were published in Pieth's 15-page final report to the FIFA executive committee, which voted for Qatar and Russia as World Cup hosts in December 2010.

After FIFA President Sepp Blatter promised to reform the scandal-hit governing body in 2011, the board appointed Pieth to lead the Independent Governance Committee advisory group which insisted on creating an independent ethics court to tackle corruption.

"This explicitly included allegations in relation to World Cup hosting decisions and the IGC singled out this issue including the decision to award the tournament to Qatar as one that required further investigation," Pieth wrote on Wednesday.

Garcia's position was supported by Pieth, who urged FIFA board members to assist the former U.S. Attorney and Interpol vice-president.

"The IGC's view was that only appointing a competent and experienced professional outsider to this role would enable FIFA fearlessly to investigate allegations of corruption at the heart of FIFA," Pieth said. "FIFA and all involved individuals must therefore fully and unconditionally co-operate with Mr. Garcia's investigation."

Moves to disrupt Garcia's probe were revealed by reformist board members who joined FIFA's hierarchy after the controversial World Cup vote.

Garcia reportedly upset some of the 13 voters who remain in office by arriving unannounced in Zurich to quiz them during a week of committee meetings.

The American lawyer and his investigating team are also seeking interviews worldwide with people who worked for the nine World Cup bid candidates, and offered anonymity to whistleblowers who had evidence of wrongdoing.

Garcia is expected to report this year to the ethics panel's judging chamber led by Joachim Eckert of Germany, which will decide any sanctions.

Though Blatter has said Russia and Qatar cannot be stripped of a tournament, it is unclear how the ethics committee could seek to use its authority.

"If allegations are confirmed, FIFA must ensure that the consequences are meaningful," Pieth wrote.

The Qatar 2022 organizing committee has denied repeated allegations of wrongdoing linked to its well-funded bid.

After fresh allegations last month implicating disgraced former FIFA board members Mohamed bin Hammam of Qatar and Jack Warner from Trinidad and Tobago, World Cup officials in the Gulf kingdom distanced them as "private individuals."

Britain's Daily Telegraph claimed Warner and his family were paid almost $2 million from a company controlled by Bin Hammam. One request for $1.2 million was dated December 2010.

Then, Bin Hammam and Warner presided over two of football's six continental confederations, with a combined 41 years' service on FIFA's board.

The "circumstances raising a suspicion that the payments were corrupt and were made in connection with the successful Qatar bid to host the World Cup in 2022 are a good example of the importance of the creation of professional and independently-led functions, such as the ethics committee," Pieth's report stated.

Summing up progress toward building public trust and being more transparent, Pieth's group praises FIFA for reaching "important milestones," including appointing Garcia, Eckert and compliance overseer Domenico Scala.

Still, the report highlights unfinished business and questions if some football leaders, including in Europe, truly want to change their "longtime privileges and well-functioning networks."

FIFA should publish salaries and bonuses, and the IGC still wants two independent outsiders to join the executive committee with voting rights. The 209 FIFA member countries will also vote on age- and term-limits, at a June 11 meeting in Sao Paulo, Brazil.

Having lost a battle which let confederations vet their own election candidates for integrity, Pieth hopes FIFA "strictly monitors their implementation and sanctions non-compliance."

The advisers completed their mandate yet want others to take on their role.

Pieth believes that "some outside independent body should continue to work with FIFA to ensure that the road to reform is completely finished."