"We confirm the neutralization of the four departments of sovereignty, including the Interior Ministry, which will not be under political parties," Rached Ghannouchi said.
President Moncef Marzouki on Friday asked Interior Minister Ali Larayedh to form a government within 15 days, following the resignation of Prime Minister Hamadi Jebali.
He quit after his own Ennahda party rejected his plan for a technocratic cabinet, excluding political parties, to prepare for elections later this year and calm unrest ignited by the assassination of secular politician Chokri Belaid on February 6.
Opposition parties had argued that putting independents in charge of the interior, foreign affairs, justice and defense ministries would improve the political climate and reduce tensions between Islamists and their critics before the vote.
Ghannouchi told Reuters in an interview this month that Ennahda was ready to negotiate on all the "sovereign" ministries, three of which it held in the outgoing government. An independent, Abdelkarim Zbidi, was defense minister. Abdelhamid Jelassi, vice-president of Ennahda said the Finance Ministry, now headed by Elyess Fakhfakh of the secular party Ettakatol, would also go to an independent.
A source close to talks on the next cabinet said this would be Slim Besbes, now a junior minister in the Finance Ministry.
Two other sources said Central Bank governor Chadli Ayari and Zbidi, the defense minister, would keep their posts in a government they said would be announced this week.
Ennahda is the biggest single party in the National Constituent Assembly, with 89 of its 217 seats. It has governed since December 2011 with two junior secular coalition partners.
(Reporting By Tarek Amara; Editing by Alistair Lyon)