Tunisian President Zine El Abidine Ben Ali has dismissed his interior minister in an attempt to quell protests which have left at least 23 people dead.
Mr Ben Ali also ordered the release of most of those detained in the protests around the country over recent weeks.
The protesters say they are angry about unemployment, poverty, corruption and government repression.
The unrest has spread to the capital, Tunis, where police have fired tear gas at gangs of youths.
At least one more person was reported to have been killed by police fire on Wednesday in a town outside the capital.
At a news conference, prime minister Mohamed Ghannouchi said the president had decided to remove Rafik Belhaj Kacem from his post, which included responsibility for policing.
Many people believe the police force has over-reacted during the protests. Mr Belhaj Kacem will be replaced by Ahmed Friaa.
Mr Ghannouchi said the president had also "announced the creation of a committee of investigation into corruption and to assess the mistakes of certain officials".
He added: "The president has decided to free all those arrested in the riots."
The prime minister gave no figure for the number of people being held. Later, the Tunisian ambassador to the UK told the BBC those guilty of "criminal activity" would not be released.
'Go away, Ben Ali'
Officials say 23 people have been killed since the protests began in the south of the country in mid-December, but human rights and trade union activists believe the number of dead to be at least 50.
On Wednesday, troops were deployed in Tunis for the first time since the civil unrest erupted.
Armoured vehicles and soldiers armed with automatic weapons were seen patrolling the city's main avenues and taking up positions outside key buildings, including the state television headquarters.
A group of protesters clashed with police at a main intersection in Tunis on Wednesday afternoon, according to the Associated Press.
There were also reports that security forces were trying to storm the headquarters of the Tunisian Labour Union's headquarters in Tunis.
The BBC's Adam Mynott in Tunis says hundreds of riot police were patrolling the Ettadamen suburb of the city and fired tear gas in an attempt to prevent protesters reaching the city centre.
The district has already seen shops ransacked, a bank set on fire and an attempted attack on a government building.
In Kasserine, a region at the centre of the unrest, a local trade union official told the BBC that all workers were observing a call for a strike.
Witnesses told the Reuters news agency that several thousand people had gathered there.
People were chanting "Go away, Ben Ali", said one witness, Mohsen Nasri. Another said local police officers had retreated to their barracks.
That came a day after disturbances in the town in which residents said a number of protesters were shot dead by police snipers. The police said they had only acted in self defence.
The state-owned channel, Tunis TV, also reported that there were "continued riots" in Tozeur on Wednesday. A correspondent said a group of people had set tyres on fire on the town's main road.
Swiss police, meanwhile, are investigating an attempt to set fire to the Tunisian embassy in Berne. The fire failed to ignite and no-one was hurt.
An anti-government protest was also held outside the embassy in Paris.
Correspondents say the interior minister's sacking is a dramatic change from just two days ago - when Mr Ben Ali said the riots were a "terrorist act" orchestrated by foreign forces - but it remains to be seen whether it will be enough to calm the situation.
On Tuesday evening, Communications Minister Samir Laabidi announced the official death toll from the past few days.
"Our numbers say there are 21 dead," he said, denying reports of a higher number of casualties. "Those who have spoken of 40 or 50 dead should produce a list of names."
Officials say two more people were killed in clashes last month, while two killed themselves in acts of protest.
Among them was 23-year-old Mohamed Bouazizi, who set himself on fire on 17 December when local officials prevented him from selling vegetables on the streets without permission, prompting the start of the protests. He died earlier this month.
Mr Laabidi also reiterated the government's claim that a fringe movement of extremists was fomenting violence, saying that "religious extremist movements and extremist movements from the left" were behind it.
The government would respond with "economic and social reforms and more opening up towards liberty", he said.
Demonstrations are rare in Tunisia, where there are tight controls aimed at preventing dissent.
The government's response to the unrest has been criticised by the EU and the US, which has demanded that freedom of expression be respected.
In its strongest statement on the violence to date, US state department spokesman Mark Toner said it was "deeply concerned by reports of the use of excessive force by the government of Tunisia".
A spokeswoman for EU foreign police chief Baroness Ashton said the violence was "unacceptable" and that those responsible had to be "identified and brought to justice".
"We are concerned about the disproportionate use of force by police against peaceful demonstrators," Maja Kocijancic said.
Mr Ben Ali is only Tunisia's second president since the country gained independence from France in 1956. He came to power in 1987 and was last re-elected to a five-year term in 2009 with 89.62% of the vote.
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