More than 400 Nepalese migrant workers have died on Qatar’s building sites as the Gulf state prepares to host the World Cup in 2022, a report will reveal this week.

The grim statistic comes from the Pravasi Nepali Co-ordination Committee, a respected human rights organisation which compiles lists of the dead using official sources in Doha. It will pile new pressure on the Qatari authorities – and on football’s world governing body, Fifa – to curb a mounting death toll that some are warning could hit 4,000 by the time the 2022 finals take place.

It also raises the question of how many migrant workers in total have died on construction sites since Qatar won the bid in 2010. Nepalese workers comprise 20% of Qatar’s migrant workforce, and many others are drafted in from countries such as India, Bangladesh, Pakistan and Sri Lanka.

A focus on the Nepalese deaths has seen Fifa and Qatar battling a PR crisis that threatens to cast a long shadow over the event. Last week, appearing before EU officials, Theo Zwanziger, a senior Fifa executive who has publicly criticised the decision to award the tournament to Qatar, pledged that his organisation would be carrying out “on-the-spot visits” to ensure that workers’ rights were being respected.

But the promise is unlikely to reassure human rights organisations and labour groups, which have raised repeated concerns about Qatar’s kafala employment system, under which migrant workers are tied to their “sponsor” employers.