Sheikh Salman's candidacy for the FIFA presidency is the subject of a legal complaint by a pro-democracy group from Bahrain.

Americans for Democracy & Human Rights in Bahrain (ADHRB) alleges that Salman - who along with UEFA secretary general Gianni Infantino is a front-runner to become the new president of FIFA on February 26 - was involved in the torture and imprisonment of pro-democracy demonstrators during the 2011 uprising in Bahrain, allegations which he strenuously denies.

ADHRB has filed a complaint to the Swiss government's contact point at the Organisation for Economic Co-operation and Development (OECD), alleging that FIFA violated provisions around human rights laid down by the OECD for multinational enterprises by allowing him to stand for the presidency.

"All the evidence suggests that Sheikh Salman was involved in the government crackdown on free expression and human rights," said Husain Abdulla, executive director of ADHRB.

"This raises serious concerns about his ability to protect the athletes that would be under his care as president of FIFA."

Another pro-democracy group, the Bahrain Institute for Rights and Democracy (BIRD), has alleged that Salman was the head of a committee which was established in 2011 to identify and apply sanctions to individuals and clubs who had been deemed to have been involved in the protest movement.

Salman has always denied that the committee ever met or took any decisions. Addressing BIRD's allegations last month, he said: "When people talk about skeletons in the closet, my closet is clear.

''Some people have an agenda, but it's a waste of time trying to answer them, and I think it has already been done by the proper bodies within FIFA and the AFC.

''There has been an integrity check and I don't have anything to defend myself about.''

A spokesperson for Salman added in a statement on Press Association Sport on Thursday night: "It is unfortunate that a few people are continuing to try to make political capital out of the FIFA election by throwing around false allegations. Sheikh Salman has always made it absolutely clear that he has done nothing wrong, and not a shred of credible evidence has ever been produced to support these historic allegations."

The OECD guidelines for multinational enterprises are not legally binding but signatory governments - including Switzerland - are required to ensure that they are implemented and observed.

The OECD said in October that FIFA was a multinational bound by its guidelines following a trade union complaint about the working conditions of labourers in Qatar building infrastructure for the 2022 World Cup.

Daniel Carey, from Deighton Pierce Glynn, the law firm which is representing ADHRB on this case, said: "FIFA is big business, and like all multinationals it has to comply with its OECD obligation to carry out effective human rights due diligence.

"Only FIFA has the authority to investigate the evidence of human rights violations but it has repeatedly failed to do so. I hope the OECD will now deal with the complaint quickly so that decisions can be taken in time for the elections."

Salman, who is the president of Bahrain's football association as well as the Asian Football Confederation, was declared as an eligible candidate for the FIFA presidency on November 9. The world governing body's ad hoc electoral committee approved him following integrity checks carried out by the investigatory chamber of FIFA's ethics committee.

Those checks, according to the FIFA website, included "a review of media reports including red flags (fraudulent behaviour, match manipulation, human rights violations, etc)" which the candidates were then asked to comment on.

Sayed Ahmed Alwadaei, the director of advocacy at BIRD, said: "The serious allegations against Sheikh Salman and his complicity in a crackdown on Bahraini footballers warranted a serious FIFA investigation.

"FIFA should now be held to account for its lack of transparency and accountability, which has allowed human rights abuses not only to flourish but to be rewarded."

Salman was endorsed as a candidate by the Confederation of African Football (CAF) last week, though it does not guarantee that all 54 member nations of CAF will vote for him in Zurich later this month.