Police fired tear gas grenades on Friday outside the interior ministry building in the Tunisian capital and gunshots were heard from nearby, prompting hundreds of protesters to flee, a Reuters reporter at the scene said.

Crowds of youth retreated a short distance from the building and started throwing stones at police, who responded by firing more tear gas grenades, the reporter added.

Demonstrators protesting against high food prices and unemployment have gathered at the building calling for President Zine al-Abidine Ben Ali to step down. Ben Ali said on Thursday he would leave office at the end of his term in 2014 amid the worst civil unrest of his 23-year rule.

As people moved away to a side street, they shouted Ben Ali, assassin. Many people had streaming eyes and were retching from the effects of the gas.

Emen Binmluka, 21, said: A bus came with police in it and they started firing tear gas. Women, children and everyone fled.

Asked about Ben Ali's promises a day earlier for greater freedoms, he said: He has always lied. We are protesting today because we know he was not telling the truth.

Outside the central bank headquarters in Tunis, soldiers guarded the building from inside an armoured personal carrier. People who fled the tear gas came up to the soldiers and were shouting at them and waving their fingers to admonish them.