Qatari authorities have freed two British researchers detained while probing the labour conditions of migrants building facilities for the 2022 World Cup, an embassy spokesperson said Tuesday.

Krishna Upadhyaya and Gundev Ghimire, who work for the Norway-based Global Network for Rights and Development (GNRD), were arrested in Doha on August 31.

A British embassy spokesperson told AFP that "we can confirm that the two British nationals have been released," without giving details.

In a statement on its website, GNRD confirmed that Upadhyaya and Ghimire were released after "eight days" in detention.

GNRD said it "had a chance to call Krishna Upadhyaya last night, and he confirmed that both he and Gundev Ghimire are doing well".

The group said it had "no details" why the pair were detained "without any access to their families or lawyers".

It added that it was trying find the first opportunity to fly them back home.

The Qatari foreign ministry said Saturday that the pair were "being interrogated for having violated provisions of the law" in Qatar.

It was unclear on what basis they where finally freed.

The pair had been carrying out follow-up research on the working conditions of migrant labourers after Qatari authorities promised a raft of reforms to address an international outcry over working conditions as the emirate prepares to host football's premier tournament.

Amnesty International had described their disappearance as "extremely worrying" and said it believed they were detained because of their work.

Earlier this year Qatar gave undertakings to improve workplace safety, housing and pay and conditions for its expatriate workforce after world football governing body FIFA came under huge pressure from rights groups to review its decision to award the emirate the 2022 World Cup.