Doha: Qatar still has work to do to improve conditions for migrant workers who are unable to leave freely and are sometimes denied days off or phones, an independent UN expert said Tuesday.

The Gulf country has previously faced criticism for inadequate legal protections afforded to hundreds of thousands of workers from developing countries working on projects ahead of the 2022 World Cup.

Independent UN rights expert Obiora Okafor said scrapping obligatory exit visas for most workers and other measures had improved conditions in Qatar where 92 percent of the labour force are migrants.

However, "against a background of Qatar making significant improvements in this area... protections for usually female migrant domestic workers continue to lag behind those of other categories," said Okafor.

The nannies and household helpers, who are often recruited from the Philippines, have not always benefited from days off or the right to change jobs and leave Qatar, he said.

"Many are denied mobile phones by employers, hindering their access to the outside world," he said.

Okafor is a Nigerian law professor whose full report on his 10 day-long fact-finding visit to Qatar will be presented to the UN's Human Rights Council in Geneva in June 2020.

UN experts are independent and do not speak for the world body, but their findings can be used to inform the work of UN organisations including the rights council.

Okafor also called on authorities to scrap the legal requirement for all migrant workers to obtain permission from their current employer before moving to a new job in the country.

"(The) requirement affects a large proportion of migrant workers," he said.

Qatar's introduction in October 2017 of a temporary $200 monthly minimum wage was a "step in the right direction", he said, but called for a "higher, non-discriminatory permanent minimum wage".

Okafor also praised Doha's relief efforts in the wake of both natural and man-made disasters around the world.

"Numerous initiatives such as the Qatar Fund For Development... are good examples of international solidarity," he said.

"Significant investment in education at home and abroad through international organisations such as UNICEF, and through regional organisations, are welcomed.

"Internationally, Qatar has been funding assistance to several refugee crises."