|Ghannouchi was prime minister for more than a decade under Ben Ali's rule, which Tunisians saw as corrupt [Reuters]
Tunisia's transitional government has said it will hold elections by mid-July at the latest, the official TAP news agency has said, quoting a cabinet statement.
The government "has decided that consultations with different political parties should not exceed mid-March ... Elections will be organised at the latest in mid-July 2011", the statement on Friday said.
The announcement came as tens of thousands of protesters rallied on Friday to demand the resignation of Mohamed Ghannouchi's, the prime minister, transitional government set up after last month's ousting of Zine El Abidine Ben Ali, the country's former president.
Demonstrators chanted "Ghannouchi leave" and "Shame on this government" as army helicopters circled above the crowd massed in the Kasbah government quarter, where police estimated that the number of people topped 100,000.
Protesters shouted "Revolution until victory" and "We will root out repression in our land".
"We are here today to topple the government," Tibini Mohamed, a 25-year-old student, told AFP news agency.
Al Jazeera's James Bays reported from Tunis said: "This is the largest protest in Tunisia since the fall of Ben Ali.
"And it shows you that even though the world's attention is now on Libya, in some of those countries that have already had a revolution, things are far from over."
Tunisians say that their revolution is an unfinished one, as one protester told Al Jazeera. "The dictator has gone but the dictatorship is still here," she told our correspondent.
And another said: "We are suffering because Ghannouchi is the same as Ben Ali."
Protests turn violent
Witnesses told the Reuters news agency that protesters burned tyres and threw rocks through the windows of the interior ministry building in the capital Tunis - long a symbol of repression under Ben Ali's more than 20-year rule.
A source at the interior ministry also told them that protesters were also destroying cars parked outside.
Meanwhile, Al Jazeera learned that tensions flared up in the central town of Kasserine, not far from Sidi Bouzid, where the protests first began in December.
Our source said that protesters have set public buildings on fire and that she had heard sounds of shooting.
Ghannouchi's caretaker government, tasked with leading Tunisia to elections due in about five months, has faced regular protests demanding it expel remnants of the old government.
Friday's was the biggest of several rallies against the transitional authority since the fall of long-time ruler Ben Ali on January 14 following weeks of demonstrations, protesters and Red Crescent workers estimated.
The interim government, tasked with organising the elections, has already undergone several changes after the protests, but Ghannouchi has remained.
He was prime minister for more than a decade under Ben Ali's rule, which Tunisians saw as oppressive and corrupt.