DOHA: The organisers of Qatar's 2022 World Cup said on Sunday they were investigating the death of an Indian labourer at one of its sites but denied it was caused by working conditions which the wealthy Gulf country is under pressure to improve.

Along with accusations of corruption during its World Cup bid, Qatar has long been under fire from rights groups for labour abuses.

Last week, world soccer body FIFA urged Qatar to hasten improvements for builders on World Cup sites and said it would monitor conditions.

Qatar, an energy exporter which has the highest income per capita in the world, is also under pressure from the United Nations to address workers' rights before World Cup construction peaks in 2017.

Labourer Jaleshwar Prasad, 48, fell unconscious on Wednesday while performing steel work at Al Bayt stadium in Al Khor, 50 km (31 miles) north of Doha, a witness told Reuters.

Organisers said the death was not caused by working conditions.

"Al Khor Hospital reported the cause of death as cardiac arrest," the Qatar's Supreme Committee for Delivery and Legacy of the 2020 World Cup said in a statement.

"The family of Mr Prasad were informed of the tragedy immediately. A full investigation is underway."

Qatar's efforts to become the competition's first Arab host have been dampened by accusations including that workers were forced to live in squalor and to work without proper access to water and shelter in the blazing sun.

About 5,100 construction workers from Nepal, India and Bangladesh are building stadiums in the country.

Unions and labour protests are banned and authorities penalise dissent with jail terms or immediate deportation.

Prasad is the third Indian employed on a World Cup site to die of a heart attack in the last six months, according to a February report by the Supreme Committee.

Qatar's Supreme Committee says there have been no work-related fatalities on World Cup sites, but law firm DLA Piper, in a review for the government in 2013, found evidence of dozens of work-related deaths among migrant labourers from South Asia.

Qatar's government has also denied claims there are higher instances of heart attacks among construction workers and does not publish independently-verified statistics on worker-related injuries and fatalities.

Autopsies and post-mortems on people who die sudden and unexpected deaths are forbidden by Qatari law unless a crime is suspected.

"Workers dying suddenly from heart attacks is something we hear about often, the causes are not always clear. But we're moving now into the hottest time of the year when the risk of fatality increases," said Amnesty Gulf researcher Mustafa Qadri.

"When a worker dies, Qatar needs to get to the bottom of what happened. People's lives are in danger".

Amnesty reported on abuses at a World Cup stadium in a wide-ranging report three weeks ago based on the accounts of 132 workers.

DLA Piper recommended that Qatar launch an independent study into cardiac deaths among migrant workers.

The head of Qatar's Supreme Committee has said Doha is working to reduce abuses he described as occurring on construction sites all over the world.