The United Nationas has called on Qatar to abolish the kafala system that ties migrant workers to their employers, a report in The Guardian newspaper said.

The call comes amid criticism of the conditions endured by those working in a construction boom in the run-up to the 2022 Qatar World Cup.

In a report by the special rapporteur on the human rights of migrants, François Crépeau, the UN general assembly has added to the pressure on Qatar to fundamentally reform and properly enforce its labour laws, the Guardian report said.

The UN report found that exploitation was "frequent", confirming that migrants often worked without pay and "live in substandard conditions", and also called for changes to the recruitment process.

Domestic workers, currently excluded from labour laws, and the majority of whom are women and girls, were "extremely vulnerable to violence and abuse," the Un report was quoted as saying.

"The recruitment process for migrants needs to be further formalised in order to prevent exploitation, and legislation must be enforced in order to ensure their rights are respected. The kafala system, which links a work permit to a single employer, is a source of abuse and exploitation of migrants and should be abolished," it said.

Qatari officials have promised that they are planning to introduce reforms, but are likely to stop short of abolishing the kafala system, the Guardian report said.

There are an estimated 1.2 million migrant workers in Qatar. Those from India make up 22 per cent of the total, with a similar proportion from Pakistan. About 16 per cent are from Nepal, 13 per cent from Iran, 11 per cent from the Philippines, 8 per cent from Egypt and 8 per cent from Sri Lanka, it said.