Hamadi Jebali of the Islamist Ennahda party was poised Saturday to become Tunisia's new prime minister under a deal struck by the country's three main parties.

Under the agreement, to be announced Monday, veteran rights activist and opposition politician Moncef Marzouki would become president, according to Abdelwaheb Matar, a senior official in the Congress for the Republic party.

The Tunisian press Saturday called it "the battle of Carthage between Marzouki and (Mustapha) Ben Jaafar" of Ettakatol, who in the end was named president of the constituent assembly, officials said.

The three parties also agreed that Ben Jaafar of Ettakatol would occupy the third key post, president of the constituent assembly, Matar told AFP, noting that the deal is subject to the approval of the assembly itself on Tuesday.

Jebali, 63, an Islamist, spent more than 15 years in Ben Ali's jails. His candidacy for the post of prime minister was announced by Ennahda a few days after the October 23 elections.

The horse trading followed Tunisia's historic democratic elections on October 23, nine months after the January ouster of dictator Zine el Abidine Ben Ali. They were the first polls staged as a result of the Arab Spring uprisings.

Editorials have been calling for the new leaders to reach agreement and get to work as the country remains in crisis and the assembly has not yet been reunited.

"Now there has been an agreement, but the essentials still have to be defined, that is, the perogatives of each of them," political analyst Salaheddine Jourchi.

Tunisians last month elected a 217-strong constituent assembly to draw up a new constitution and appoint the caretaker government until the country calls a general election.

Ennahda won the most seats, with 89.

It put forward Jebali for prime minister as it went into talks with the leftist Congress for the Republic, which won 29 seats, and Ettakatol, which won 20, over who should occupy the senior political posts.

The deal was also confirmed by a leading figure inside Ettakatol, who cautioned that the discussions about the prerogatives of the future leaders had not ended.

He said an official announcement on the nominations would be made "by Monday" as talks would continue over the weekend about sharing out portfolios in the government.

The first task of the constituent assembly is to draw up a new constitution for the country after the ouster of Ben Ali by a popular uprising on January 14. The new executive will run Tunisia until general elections are called.

The Ennahda party, which vowed to pursue moderate policies after it won the elections, has provoked concern about its radical roots by evoking the caliphate and criticising single mothers.

Last Sunday, Jebali, Ennahda's number two official, alarmed some by bringing up "the caliphate", an Islamic system of government based on sharia law.

Marzouki, another former opponent of the regime, is a 66-year-old doctor who spent 10 years living in exile in France before returning to Tunisia after the revolution. His party describes itself as being nationalist left.

Ben Jaafar, another doctor aged 71, heads the leftist Ettakatol (Forum) party.