Protesters pressured Tunisia's new interim government to quit on Tuesday in the wake of president Zine El Abidine Ben Ali's ouster, as the cabinet prepared a major shake-up and a top US envoy visited.

Hundreds of protesters from impoverished regions in central Tunisia chanted anti-government slogans in front of Prime Minister Mohammed Ghannouchi's offices for a third day, saying they would not leave until the cabinet resigns.

The new government has announced unprecedented democratic freedoms for Tunisia after the end of Ben Ali's 23-year rule, but many people are angry that figures from the previous regime, like Ghannouchi, remain in the cabinet.

Protesters also want Ben Ali's powerful RCD party to be disbanded.

Army chief Rachid Ammar on Monday waded into the crowd of protesters and asked them to leave, warning a "power vacuum" could lead to dictatorship and promising the army would be a "guarantor" for the revolution.

But hundreds ignored his plea and spent a second night camped out in the government quarter in defiance of a curfew that was decreed under Ben Ali and has stayed in force as the government struggles to restore order.

"The battle will play out in Tunis. That's why we've come here. To bring down the government. We have to clean up everything," Lotsi Abbes, a chemist from southern Tunisia, told AFP after a night on the square.

Mehrezia Mehrez, from the industrial city of Kasserine in central Tunisia that saw some of the deadliest clashes of the uprising that forced out Ben Ali, said: "They have to go, we will stay here until they go."

There were violent scenes at the rally on Monday, as security forces fired tear gas and sealed off the area with barbed wire. Some of the protesters threw stones, charged against police lines and smashed up a police car.

The government meanwhile said it was releasing 260 million euros (355 million dollars) for public works projects in central Tunisia and to compensate the families of the dozens of people killed during Ben Ali's crackdown on the month-long uprising.

Taieb Baccouch, a spokesman for the government and the education minister, also told AFP on Monday that a cabinet reshuffle involving at least six new ministers was under discussion and could be announced on Tuesday.

Five ministers have already resigned and Tunisia's main trade union, the General Union of Tunisian Workers (UGTT), which played an instrumental role in the anti-Ben Ali protests, has refused to recognise the government.

US Assistant Secretary of State Jeffrey Feltman, the top-ranking US official on the Middle East, meanwhile arrived in the capital on Monday to press the caretaker government on democratic reforms and new elections.

"We're prepared to provide any support that would be needed or requested," he said after meeting Foreign Minister Kamel Morjane.

"We have heard the voice of the Tunisian people loud and clear," he said.

Feltman, who was due to leave Wednesday after further consultations, is the first senior foreign official to visit Tunisia since Ben Ali's downfall.

The visit was likely to prove controversial, especially after a newspaper article in the popular French-language daily Le Quotidien on Tuesday alleged, without any sourcing, that the new government was controlled by Washington.

Tunisia is still in the midst of upheaval and many schools and universities, shut down by Ben Ali in a failed bid to stop the protests widening, have remained closed despite orders to begin re-opening this week.

Ghannouchi, who has been the prime minister since 1999 and is seen as a moderate, has said he will resign but only after organising the north African state's first democratic elections since independence from France in 1956.

He said the vote could be held in the next six months but has not set a date and under the constitution the vote should take place within two months.

Ben Ali fled to Saudi Arabia on January 14 amid a wave of protests that began when a 26-year-old fruit vendor set fire himself to protest police abuse.

The Arab world's first popular revolt in recent history has triggered similar protests across the region, particularly in Algeria, Egypt and Yemen.

Egypt braced for a day of nationwide anti-government protests on Tuesday, with organisers counting on the Tunisian uprising to inspire the crowds.