Qatar's top World Cup official said Tuesday that more than 400 migrant workers died in labour accidents in the country in the years leading up to the tournament.

Hassan Al-Thawadi, head of Qatar's delivery and legacy organising committee, gave the figure of 400-500 in a British television interview when asked how many workers had died "doing work for the World Cup".

The organising committee said his response referred to "national statistics covering the period of 2014-2020 for all work-related fatalities" in Qatar "covering all sectors and nationalities".

It said there were 414 worker deaths over the eight-year period.

Migrant workers make up more than 2.5 million of Qatar's 2.9 million population and labour conditions have been strongly criticised -- particularly on the huge construction projects that have transformed the tiny Gulf state in the past decade.

Qatar has never given precise figures for the number of deaths of foreign labourers though it has denied claims by rights groups that thousands died.

Authorities have insisted that only 37 workers on World Cup projects have died -- and only three in work-related accidents -- and Thawadi repeated this figure in the interview.

"One death is a death too many. Plain and simple," Thawadi said.

His comments brought new condemnation from rights groups however.

"Over the last decade, thousands of workers have returned home in coffins, with no explanation given to their loved ones," said Steve Cockburn of Amnesty International.

"Qatar’s extreme heat and gruelling working conditions are likely to have contributed to hundreds of these deaths, but without full investigations the true scale of lives lost can never be known."

Under pressure from international unions, Qatar has undertaken reforms that have been praised.

It has dismantled its 'kafala' labour system which gave employers powerful rights over whether workers could leave their jobs or even the country.

It has also introduced a minimum wage of 1,000 riyals ($260) and restricted hours in which workers can go out in extreme heat.

A series of ministers who have been through Qatar for the World Cup in recent days, including US Secretary of State Antony Blinken, have acknowledged the progress but said more must be done.