Ali Larayedh, the Islamist politician tapped on Friday to become Tunisia's next prime minister and who was tortured under ousted dictator Zine El Abidine Ben Ali, is seen as a moderate and a man of dialogue.

He will attempt to form a government at a time of political crisis in Tunisia, with divisions between liberals and Islamists deepened by the assassination earlier this month of leftist opposition leader Chokri Belaid.

Larayedh, 57, has belonged to the Islamist party Ennahda since it was founded in 1981 and was president of its Shura (consultative) Council in the early 1980s, before rising to the head of its political bureau.

The former naval engineer was arrested in 1987 at the end of Tunisian founding president Habib Bourguiba's rule, and sentenced to death.

When Ben Ali seized power months later, he was pardoned along with other Islamists on death row, but arrested again in 1990 and eventually jailed for 15 years, 13 of which he spent in isolation.

The Islamists were repressed during Ben Ali's reign, and Larayedh was tortured in prison like many of his colleagues in Ennahda which now rules Tunisia.

The former regime threatened to infect him with the AIDS virus and to publish a pornographic video of him and another man in a campaign to discredit him.

His wife Ouidad, with whom he has three children, suffered sexual violence in prison, which was filmed in order to put pressure on her husband, according to the International Federation for Human Rights (FIDH).

Ennahda triumphed in Tunisia's first free elections, in October 2011, 10 months after the uprising that toppled Ben Ali, and became the main party in the coalition government, taking the key interior, foreign and justice ministries.

Larayedh, with his thick black moustache and glasses, was appointed head of the interior ministry, which for years had persecuted him and his party.

"I almost died several times in the jails of the interior ministry. But I mark the difference between that period and now. The revolution came to advance and establish a transitional justice and not to seek vengeance," he said at the time.

Hailing from Medenine in Tunisia's far south, Larayedh is considered open to dialogue and a member of Ennahda's moderate wing, like his predecessor Hamadi Jebali, whose resignation laid bare divisions with the Islamist party.

Opposition leaders have praised him for being reasonable, compared with other senior Islamists of his generation.

When he was appointed interior minister, he said he wanted to make his ministry a springboard for strengthening ties with Maghreb countries and economic partnerships with Western powers, notably France and the United States.

But his achievements in government over the past 14 months have been mixed, with accusations frequently levelled against him of complacency towards the rising threat of violence from Tunisia's hardline Salafist movement.

As well as the rise of radical Islamists, Tunisia has been prey to ongoing social unrest since the revolution over the government's failure to improve living conditions.

With deadlock over the new constitution as parliament squabbles over the nature of the country's future political system, any new prime minister has his work cut out.