Migrants who have worked for nearly a year without pay on a Qatar skyscraper are facing "severe food shortages" and cannot leave or seek other employment, Amnesty International said Wednesday.

Qatar has come under mounting criticism from rights groups, particularly after being chosen to host the 2022 World Cup, which has spotlighted the conditions of migrant workers in the gas-rich monarchy's booming construction industry.

Amnesty urged Qatari authorities to address the plight of 80 migrant workers, mostly from Nepal, who are working for the Lee Trading and Contracting (LTC) company, saying they are "working in conditions that may amount to forced labour."

“They have not been paid for nearly a year and can’t even buy food to sustain themselves on a day-to-day basis. They also can’t afford to send money back home to their families or to pay off debts," said Salil Shetty, secretary general of Amnesty International.

The group includes around 60 Nepalese workers as well as others from Sri Lanka, the Philippines, Nigeria, China and Bangladesh.

They have been working on floors 38 and 39 of Doha's Al-Bidda Tower, known as "Qatar's Home of Football" because a number of sports organisations have offices there, Amnesty said.

Amnesty said it had seen documentation showing LTC owes the workers around 1.5 million riyals ($412,000, 300,000 euros) for the work, which was completed in October.

"'Do the work and we’ll pay you tomorrow,' they said," Amnesty quoted a Nepalese labourer as saying.

"We kept doing the work and they kept changing the date and we never got paid.”

The rights group said the workers had filed cases against LTC in Doha's Labour Court but were asked to pay fees of 600 riyals ($165) each for their cases to proceed.

The workers told Amnesty the court rejected their petitions for the fees to be waived, and Amnesty said under Qatari law they should have been exempted from the start.

Amnesty said the workers are facing severe food shortages after the company stopped giving them a 250-riyal ($69) monthly food allowance in October, and that last month several of the men complained of hunger.

Neither government spokesmen nor LTC representatives could be reached for comment on Amnesty's findings.

But Amnesty quoted an LTC representative as saying that the food allowance had stopped because, "at the end of the day, I'm not making any money out of this company."

Amnesty also cited a company representative as saying the firm was unable to pay for residency permits for the workers, leaving them vulnerable to arrest.

Because of Qatar's restrictive sponsorship system, the workers are unable to seek employment at another company.

Qatar last month said foreign allegations of abuse of migrant workers working on World Cup facilities were "exaggerated" but insisted it took such claims seriously.