Two British human rights activists have "disappeared'"in Qatar while investigating the treatment of the country's migrant workforce. The Global Network for Rights and Development (GNRD), which employs the men, has not heard from them for more than four days and fears that they may have been detained.

Krishna Upadhyaya, 52, and Ghimire Gundev, 36, arrived in Qatar on 27 August to research a forthcoming report on the working and living conditions of Nepalese migrant workers in the Gulf emirate. Qatar's treatment of its migrant workers has drawn widespread criticism from human rights groups as it prepares to host the 2022 World Cup.

On the evening of Saturday August 30, Upadhyaya sent an urgent text to a friend in Norway saying, "I am being followed by the police here. Looks like they will give me troubles now."

Evgenia Kondrakhina, chief executive of GNRD, a human rights and development organisation based in Norway, said that despite repeated attempts to contact the Qatari authorities, "we have not received any response from any Qatari, officially or unofficially."

The last contact GNRD had with the two men was on the morning of Sunday 31 August as they prepared to leave their hotel for the airport. According to GNRD, after checking out, they chose to remain in the reception because they felt too unsafe to leave the hotel premises.

Upadhyaya had apparently, "expressed alarm at the number of police in the vicinity, and noticed undercover authorities who came extremely close to him whenever he spoke on the phone". The airline they were due to fly with confirmed they did not board the plane.

Kondrakhina said: "GNRD holds the Qatari authorities responsible for their safety. In the event that its employees are subjected to any kind of physical or psychological harm, GNRD is prepared to take all necessary legal action."

Upadhyaya, who is from Nepal, is an experienced human rights researcher and worked for Anti-Slavery International for almost 12 years.

Aidan McQuade, director of Anti-Slavery International, said of Upadhyaya: "He's animated by a profound commitment to social justice, which has most explicitly been expressed through his work in the struggle for democracy in Nepal and against the forced labour and enslavement of vulnerable workers across the world."

Upadhyaya's wife, Sarita Poudyal, who lives in London, said: "I'm feeling very sad. The Qataris need to send him back as soon as possible and we need to know the reason why this has happened.

"I think they don't want the news about the way they treat migrant workers to reach the outside world."