Human rights organisations have reacted with alarm to the Bahraini royal Sheikh Salman bin Ebrahim al-Khalifa becoming the new favourite to succeed Sepp Blatter as Fifa president, citing his family’s role in the brutal suppression of the country’s pro-democracy demonstrations in 2011.

Sheikh Salman, the Asian Football Confederation president, is expected to announce his candidature early next week after agreeing to fill the void created by the suspension of the Uefa president, Michel Platini, over an alleged “disloyal payment” from Blatter, who has also been suspended by world football’s governing body. Sheikh Salman has received backing from football associations around the world, including many in Platini’s Uefa stronghold.

But human rights organisations have reacted furiously, resurrecting claims that Sheikh Salman was involved in identifying athletes involved in pro-democracy demonstrations in 2011, some of whom were then allegedly imprisoned and tortured. “Since the peaceful anti-government protests of 2011, which the authorities responded to with brutal and lethal force, the al-Khalifa family have overseen a campaign of torture and mass incarceration that has decimated Bahrain’s pro-democracy movement,” said Nicholas McGeehan, the Gulf researcher at Human Rights Watch.

“If a member of Bahrain’s royal family is the cleanest pair of hands that Fifa can find, then the organisation would appear to have the shallowest and least ethical pool of talent in world sport.”

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Sheikh Salman, who has always denied those allegations, will be presented as a “clean skin” candidate, having been elected to the Fifa executive committee only in 2013 and so not tarnished by the decades of allegations of corruption and malpractice that have built up at its door.

Sheikh Salman is believed to have already secured expressions of support from Europe, Asia, Africa and South America as it has become increasingly clear Platini is highly unlikely to make it on to the ballot paper by the 26 October deadline.

The Football Association on Friday suspended its support for Platini’s bid to become Fifa president after a briefing from his lawyers at Uefa’s headquarters in Nyon. The FA has been under huge pressure to reconsider its position after the Uefa president was questioned by the Swiss attorney general as somewhere “between a witness and an accused person” over a £1.35m payment received from the departing Fifa president, Blatter, in 2011. As the Guardian revealed this week no written contract exists for the £1.35m payment, which relates to the period between January 1999 and June 2002 when Platini acted as a paid adviser to Blatter. Blatter confirmed as much on Friday, describing the payment as a “gentleman’s agreement”.

Sources in the region have suggested Sheikh Salman would not have agreed to run, having initially promised to back Platini, if he did not believe he would win.

Prince Ali, the Jordanian Royal who lost to Blatter in May days before the 79-year‑old was forced to promise to stand down in the face of a spiralling corruption crisis, is currently the only other declared candidate. Sheikh Salman, who has the backing of the influential Kuwaiti Fifa executive committee member Sheikh Ahmad al-Fahad al-Sabah, will immediately be installed as the strong favourite to succeed Blatter.

However, he will have to deal with renewed interest in allegations surrounding his role in the brutal suppression of pro-democracy protests in the country in 2011, for which the ruling al-Khalifa regime was widely criticised.

The Guardian has seen a letter from the Bahrain Institute for Rights and Democracy in which it called on Michael Garcia, then head of the investigatory unit of the Fifa ethics committee, to investigate Sheikh Salman’s role in “systematically targeting and mistreating athletes who have taken part in anti-government protests”.

Associated Press reported in 2011 that more than 150 athletes, coaches and referees were jailed after a special committee, which it said was chaired by Sheikh Salman who was then head of the Bahrain Football Association, identified them from photos of protests. The BIRD claimed that in doing so he had broken Fifa’s Code of Ethics. But Garcia wrote back in January 2014 to say that the claims made by BIRD were outside the investigatory chamber’s jurisdiction.

In response BIRD pointed to a string of Fifa decisions in which it had opened proceedings against national associations because of government interference.

“Fifa has a statutory duty to protect the integrity and reputation of football in Bahrain,” it added, but again Garcia refused to open an investigation. “In attempting to get rid of its corruption crisis Fifa is now set to replace one allegedly corrupt official with another,” said Sayed Al Wadaei, director of advocacy at BIRD.

“Salman is accused of involvement in a campaign of abuse against athletes in Bahrain, something Fifa is aware of and has refused to investigate. Salman’s appointment would be absurd.”

After his election as AFC president in May 2013 Sheikh Salman said there was no proof that he was involved in identifying protesters. “I just have one question: You talk about allegations but the question is, do you have the proof?” he said.

“Somebody talks about the government, I don’t think this is our business in football. If anybody has the proof that the Bahrain Football Association has violated the statutes of Fifa or AFC, then present it. Otherwise we move on.”In the wake of the 2011 protests, new human rights insititutions were set up based on the recommendations of the Bahrain Independent Commission of Inquiry but an Amnesty report in April of this year claimed they had had little effect in practice. Among those footballers seized were the country’s record goalscorer Alaa Hubail and his brother Mohammed Hubail. Alaa Hubail was interrogated on state television and called a traitor. Both were allegedly tortured. “What happened to me was a cost of fame. Participating in the athletes’ rally was not a crime,” he told AP at the time.

Along with other players, they were barred from playing for their clubs and the national team. Amnesty’s Bahrain researcher Said Haddadi said that, like other Gulf states, Bahrain was looking to sport to burnish its image.

“They like to project an image of a country that is at peace with itself. But that is not the case. You only have to hear what is happening against political activists or anyone who criticises the authorities,” said Haddadi.

The AFC and Sheikh Salman’s office did not respond to requests for comment. He is expected to travel to Zurich on Monday before Tuesday’s emergency Fifa executive committee meeting, chaired by the interim Fifa president, Issa Hayatou, in the absence of the suspended Blatter.