A damning Amnesty report has raised fresh fears about the exploitation of the migrant workers building the infrastructure for the 2022 World Cup in Qatar, amid a rising toll of death, disease and misery.

The report – published a week after Fifa's president, Sepp Blatter, met the country's emir and declared Qatar was "on the right track" in dealing with workers' rights – claims that some migrant workers are victims of forced labour, a modern form of slavery, and treated appallingly by subcontractors employed by leading construction companies in a sector rife with abuse.

The report, based on two recent investigations in Qatar and scores of interviews, found workers living in squalid, overcrowded accommodation exposed to sewage and sometimes without running water. It found that many workers, faced with mounting debts and unable to return home, have suffered "severe psychological distress", with some driven to the brink of suicide. Discrimination is common, according to the report, which says that one manager referred to workers as "the animals".

It describes one case in which the employees of a company delivering supplies to a construction project associated with the planned Fifa headquarters during the 2022 World Cup were subjected to serious labour abuses. Nepalese workers employed by the supplier said they were treated like cattle. Employees were working up to 12 hours a day, seven days a week, during the summer months when temperatures regularly reach 45C.

Qatar's labour laws stipulate a maximum working day of 10 hours and say no one should work between 11.30am and 3pm during the summer months.

Last month Fifa was forced to address the issue of workers' rights after a Guardian investigation showed that dozens of Nepalese workers had died in recent months, prompting warnings from trade union organisations that 4,000 could be killed before the start of the football tournament.

Blatter promised to travel to Doha to meet the emir, Sheikh Tamim bin Hamad bin Khalifa al-Thani, and said he would raise the issue of workers' rights. But after the meeting and a presentation from the 2022 World Cup supreme committee, which includes many senior government representatives, Blatter said he was reassured by the progress that had been made on the issue.

That will not pacify human rights organisations, which have called for improvements to living and working conditions and for urgent action to reform the kafala sponsorship system that ties migrant workers to their employers. Amnesty said the sponsorship system "permits abuse and traps workers".

In November 2011, the Fifa general secretary, Jérôme Valcke, met Qatari officials to address the issue of workers' rights and the Qatari authorities promised to take the issue seriously.

But Amnesty's report, The Dark Side of Migration: Spotlight on Qatar's Construction Sector Ahead of the World Cup, is based on inspection visits in October 2012 and March 2013 and suggests change is nowhere near fast enough, despite a new charter introduced by the supreme committee, which applies only to the World Cup stadiums and not to infrastructure.

Amnesty said many workers had reported poor health and safety standards at work, including some who said they had not been issued with helmets on sites.

It quoted a representative of Doha's main hospital saying that more than 1,000 people were admitted to the trauma unit in 2012 after falling from height at work. Some 10% were disabled as a result and the mortality rate was significant.

Researchers also found migrant workers living in squalid, overcrowded accommodation with no air conditioning, exposed to overflowing sewage or uncovered septic tanks. One large group was found to be living without running water.

The organisation has also documented cases where workers were effectively blackmailed by their employers to get out of the country and others where they were not allowed to leave.

Researchers witnessed 11 men signing papers to get their passports back to leave Qatar in front of government officials, falsely confirming that they had been paid.

The company for which the men worked, ITC, had cashflow problems and 85 workers from India, Nepal and Sri Lanka were left in accommodation with no electricity or running water, with sewage leaking from the ground and piles of rubbish accumulating. Their salaries went unpaid for up to a year and they were forced to sign away any claim to the money before being allowed to leave.

"It is simply inexcusable in one of the richest countries in the world that so many migrant workers are being ruthlessly exploited, deprived of their pay and left struggling to survive," said Amnesty's general secretary, Salil Shetty.

"Our findings indicate an alarming level of exploitation in the construction sector in Qatar. Fifa has a duty to send a strong public message that it will not tolerate human rights abuses on construction projects related to the World Cup."

Amnesty, which carried out interviews with 210 workers and held 14 meetings with Qatari authorities, said that multinational construction firms profiting from the $220bn (£137bn) construction boom in the tiny gas-rich state could not ignore the actions of the web of subcontractors employed to do the work.

"Construction companies and the Qatari authorities alike are failing migrant workers. Employers in Qatar have displayed an appalling disregard for the basic human rights of migrant workers. Many are taking advantage of a permissive environment and lax enforcement of labour protections to exploit construction workers," said Shetty.

Amnesty found that some of the workers who had suffered abuses were working for subcontractors employed by global companies, including Qatar Petroleum, Hyundai E&C and OHL Construction.

"Companies should be proactive and not just take action when abuses are drawn to their attention. Turning a blind eye to any form of exploitation is unforgivable, particularly when it is destroying people's lives and livelihoods," added Shetty.

Following his meeting, Blatter said Fifa could look forward to "an amazing World Cup" in Qatar. "What was presented to us shows that they are going forward not only today but have already started months ago with the problems with labour and workers. The labour laws will be amended and are already in the process of being amended."

The Qatari authorities insist they are being proactive and say the World Cup can be a catalyst for change.