Amnesty International says a blogger and human rights activist has been detained incommunicado in Qatar and is at risk of torture or other ill-treatment.

The UK-based human rights group said Sultan al-Khalaifi was arrested on March 2 by around eight individuals in plain clothes, believed to be members of the security forces.

According to information received by Amnesty International, al-Khalaifi had told his wife earlier that day that state security had contacted him, asking him to report to them, but that he did not know why.

The reasons for his detentions and his whereabouts are unknown, Amnesty said in a statement on Friday, adding that it is believed he is being held in the custody of state security.

Amnesty said al-Khalaifi is the founder of a rights group which campaigns primarily on cases of detention in Qatar, but is legally registered in Switzerland.

In the latest entry available on his blog, al- Khalaifi makes critical comments about book censorship in Qatar.

Speaking to Al Jazeera, Najib al-Nuaimi, al-Khalaifi's lawyer, said: "This gentleman is Sultan al-Khalaifi, he is being detained with three others.

"It's just for expressing his own opinion, it must be, because [he] was detained three, four, or ten times already by special security and he's still insisting in his own opinion.

"I think the mistake here is that there is a law, which I call a criminal law, if I can say.

"The law itself is criminal, because it allows the minister of interior to detain anyone, anywhere, for six months, extendable for another six months, without a trial, without any lawyer, it's up to him."‎

The Qatari government could not be contacted for comment.