More than 450 Indian migrants working in Qatar have died in the last two years, according to new data from the Gulf state which is under pressure over its rights record ahead of the 2022 World Cup.

In response to a Right to Information request filed by AFP, the Indian embassy in Qatar gave figures detailing the number of deaths in 2012 and the first 11 months of 2013.

On average about 20 migrants died per month, peaking at 27 in August last year. There were 237 fatalities in 2012 and another 218 in 2013 up to December 5.

The embassy did not give any details about the circumstances of the deaths, but the International Trade Union Confederation said the data showed an "exceptionally high mortality rate."

The bad publicity surrounding Qatar's record on worker rights has until now mostly been focused on Nepalese workers whose plight has been highlighted in a string of media reports.

An official at the Nepalese embassy in Doha told AFP last month that 191 deaths had been registered in 2013, many of them from "unnatural" heart failure, compared with 169 the year before.

One construction worker who spoke to AFP after returning to Nepal said he had had his passport confiscated and was forced to work from dawn to dusk, often without a protective helmet or gloves.

The Guardian newspaper group reported at the weekend that human rights group Pravasi Nepali Co-ordination Committee had concluded that 400 Nepalese workers had died on Qatar's building sites.

Most of the labourers working on the new stadiums and vast infrastructure projects ahead of football's biggest tournament in the wealthy Gulf state are from South Asia.

"Qatar is choosing to prolong the system of modern slavery which is the root cause of the incredibly high death toll for workers," ITUC secretary general Sharan Burrow told AFP in a statement.

The ITUC, which has pioneered opposition to Qatari labour law, estimates that as many as 4,000 workers might die on World Cup building sites before a ball is kicked in 2022.

Oil- and gas-rich Qatar has a "kafala" system which means migrants are sponsored by an individual who then exerts enormous control over their lives and leaves some workers trapped.

The case of French footballer Zahir Belounis highlighted the system last year when he finally left Doha after being stranded for a year as his club Al-Jaish had refused to grant him an exit permit.

On February 11, the Gulf state issued new guidelines aimed at protecting expatriate workers, suggesting they should be paid properly and promptly and housed adequately.

Amnesty International said in November that workers were being treated like "animals," and urged football's world governing body FIFA to press Qatar to improve conditions.

FIFA executive committee member Theo Zwanziger said last Thursday that the World Cup could help improve the country's "appalling" human rights record by inviting closer scrutiny.

The embassy in Qatar says that the exact number of Indians in Qatar is unknown, but it was estimated at close to 500,000 at the end of 2012, about 26 percent of Qatar's total population.

Under India's Right to Information law, government bodies are bound to hand over information requested by members of the public or journalists providing it is not harmful to the national interest.

AFP also asked to see any any correspondence between the embassy and the Indian government regarding the treatment of its nationals, but this request was declined.

An Indian foreign ministry was not immediately available for comment. (AFP)