Qatar has confirmed it is holding two British researchers who had been probing the labour conditions of migrants building facilities for the 2022 World Cup, saying they "violated" the emirate's laws.

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

The Qatari foreign ministry said in a statement the pair were "being interrogated for having violated provisions of the law" in Qatar, but it did not elaborate.

"All of the actions that have been taken against the two Britons are consistent with principles of human rights enshrined in the constitution", said the statement, released by the official QNA news agency late Saturday.

It said a representative of the British embassy in Doha had visited the two.

On its website, GNRD said that a British authority representative had transferred a message from Upadhyaya to his family saying: "I am well, I have been well looked after and I will be home soon."

"We have been arrested due to problems with our paperwork," he was quoted as saying.

Rights watchdog Amnesty International raised concerns on Thursday about the pair's "enforced disappearance," saying they went missing after checking out of their hotel in Doha.

They 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 described their disappearance as "extremely worrying" and said it believed they had been detained because of their work.

GNRD said Wednesday that two British staffers had disappeared in the Qatari capital after complaining of being followed and "harassed" by police.

A British embassy spokesperson contacted by AFP on Sunday said that "we are providing consular assistance" to the two Britons, without giving further details.

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.