Tunisia's detained former justice minister Noureddine Bhiri is refusing food or medication after his transfer to hospital, a member of a delegation that visited him told AFP on Monday.

Bhiri, deputy president of the Islamist-inspired Ennahdha party, which President Kais Saied views as an enemy, was arrested by plainclothes officers Friday and his whereabouts were initially unknown.

Ennahdha had played a central role in Tunisia politics until a power grab by President Kais Saied last year.

Tunisia was the only democracy to emerge from the Arab Spring revolts of a decade ago, but civil society groups and Saied's opponents have expressed fear of a slide back to authoritarianism a decade after the revolution that toppled longtime dictator Zine El Abidine Ben Ali.

On Sunday activists and a former Ennahdha legislator said Bhiri was in a critical condition and facing death.

But the source told AFP that Bhiri, 63, is "not in critical condition for the time being".

The source, asking not to be named, told AFP that a joint team from Tunisia's independent anti-torture group INPT and the United Nations rights commission visited Bhiri at hospital in the northern town of Bizerte on Sunday.

He is "lively and lucid", and being kept under close observation in a private room of the hospital's cardiology ward.

Since Friday, however, Bhiri has "refused to take any food or medication, prompting his transfer to hospital" two days later, the source said.

Samir Dilou, a lawyer and ex-Ennahdha MP, condemned Bhiri's arrest as "political" and an abuse of the justice system.

Senior Ennahdha politician Noureddin Bhiri, pictured in 2012, is not in critical condition "for the time being" after his detention, a source said
Senior Ennahdha politician Noureddin Bhiri, pictured in 2012, is not in critical condition "for the time being" after his detention, a source said AFP / Fethi Belaid

He told a Tunis news conference that he is lodging a "kidnapping" charge against Saied and Interior Minister Taoufik Charfeddine.

Bhiri's wife, Saida Akremi, also a lawyer, told reporters he had suffered "a heart attack", and that she was being denied access to him because she refused to sign documents as demanded by security services.

Mondher Ounissi, a doctor and member of Ennahdha's executive bureau, said Sunday that Bhiri suffers from several chronic illnesses, including diabetes and hypertension.

He has been "deprived of his medication" and "his life is threatened", Ounissi said, adding that Bhiri usually takes 16 pills a day.

The interior ministry on Friday said that two individuals had been ordered under house arrest, without identifying them.

It said the move was a "preventive measure dictated by the need to preserve national security".

The anti-torture group INPT has identified the second person detained as Fathi Baldi, a former interior ministry official.

The president "bears full responsibility for the life of Mr Bhiri", the anti-Saied group "Citizens against the coup" said Sunday on Twitter.

It said he had been "rushed to the hospital in a very serious condition".

Saied on July 25 sacked the Ennahdha-supported government and suspended parliament, presenting himself as the ultimate interpreter of the constitution.

He later took steps to rule by decree, and in early December vowed to press on with reforms to the political system.