A prominent figure in Tunisia's Salafist movement, Mohammed Bakhti, died on Saturday after going on hunger strike over his arrest for an attack on the US embassy, in the second such death this week, his lawyer said.
"He died in hospital at around 2 am (0100 GMT)," said Abdelbasset Ben Mbarek, noting that his death followed that of another member of the hardline Islamist movement, Bechir Gholli, who died on Thursday also after refusing food for nearly two months.
The lawyer had warned for several days that Bakhti, who was suffering from a brain haemorrhage, was in critical condition.
The moderate Islamist party Ennahda, which heads Tunisia's ruling coalition, called for a "rapid and transparent probe" to determine "the circumstances of the arrests and detentions as well as the causes of death and the hunger strikes."
After the latest death, a justice ministry official said on Saturday that three of 56 Tunisian prisoners on hunger strike were in a "more or less worrying condition," having refused to eat for exactly one month.
Negotiations are taking place with the detainees, their families and civil society groups to persuade them to call off their hunger strike, he told AFP.
The official said most of the hunger strikers, not all of whom are Islamists, started their protest between November 9 and 16, and denied a claim from lawyer Mbarek that between 300 and 400 prisoners had started a hunger strike in solidarity.
Bakhti and Gholli began their strike in late September, days after their arrest in connection with a September 14 attack on the US embassy by a crowd of Islamists during which four assailants were killed in clashes with security forces.
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They insisted they were innocent and protested over the conditions of their detention, while the Salafist movement charged it was being victimised by the authorities.
Bakhti was considered a senior figure in the jihadist movement and close to Abu Iyad, the alleged organiser of the embassy attack, who is on the run.
Justice Minister Noureddine Bhiri of Ennahda said on Friday that Bakhti had been released on November 11. "His health deteriorated after his release," he said.
But Ben Mbarek said that Bakhti had been in a coma and was dying. The decision to free him was taken because the authorities knew "he was about to die," he said.
Bakhti was jailed for 12 years in 2007 over bloody clashes between the army and Islamists in Soliman, near Tunis, under Zine El Abidine Ben Ali's regime but released under an amnesty declared after the 2011 revolution.
In the attack on the US mission, hundreds of protesters, angry over an anti-Islam film made in the United States, stormed the sprawling embassy compound in a suburb of Tunis.
More than 100 people were detained following the attack.
Tunisia's hardline Islamists have carried out numerous acts of violence since last year's revolution that ousted Ben Ali.