Tunisia's main political parties have accused the president of staging a coup after he sacked the prime minister and suspended parliament.
Kais Saied, who also dismissed the defence minister, says he acted in accordance with the constitution.
The move followed Sunday's violent mass protests over the government's handling of the coronavirus outbreak and the economic and social turmoil.
Calls are now growing from the international community for restraint.
The European Union urged all political sides in Tunisia to respect the rule of law and avoid violence. There were similar appeals from the Arab League, Russia and Qatar.
Clashes among Mr Saied's supporters and opponents continued on Monday in the capital Tunis.
They threw stones at each other outside the legislature, which has been barricaded by troops.
Mr Saied, an independent who was elected in 2019, has had a long-standing feud with the man he has removed, Prime Minister Hichem Mechichi. Mr Mechichi has the backing of the largest party in parliament, Ennahda.
Tunisia's revolution in 2011 is often held up as the sole success of the Arab Spring revolts across the region - but it has not led to stability economically or politically.
The recent spike in Covid cases has fuelled long-standing public frustration. The health minister was sacked last week after a bungled vaccination drive.
Statesman or dictator?
On Sunday, thousands of people across Tunisia demonstrated against the PM and Ennahda, the moderate Islamist party.
Its local headquarters in the south-western city of Touzeur were set on fire.
In a televised address, Mr Saied said: "We have taken these decisions... until social peace returns to Tunisia and until we save the state".
He vowed to respond to further violence with military force.
In the early hours of Monday, the speaker of parliament, Rached Ghannouchi, who leads Ennahda, tried to get into the legislature. When he was blocked by Mr Saied's supporters, he and his own loyalists staged a sit-down protest.
Later on Monday, Al-Jazeera TV, which has been viewed as sympathetic to Ennahda, said security forces had raided its offices in Tunis, unplugging all equipment and telling staff to leave.
'Coup against Tunisia's revolution'
Ennahda and two other opposition parties have accused Mr Saied of carrying out a coup.
He and Mr Mechichi have been in conflict for a long time.
Mr Saied has said he will now govern alongside a new PM, with parliament suspended for 30 days.
He cited the constitution as backing for his actions, but the legal framework is unclear.
As the largest party in parliament, Ennahda has the right to nominate the PM.
Covid flare-up
Coronavirus-related deaths reached a record for the country last week, passing 300 in one 24-hour period. Tunisia has one of the highest per capita death rates in the world.
Vaccinations have been slow: only 7% of the 11.7 million population are fully vaccinated.
The government recently attempted to speed up vaccination by opening it to all over-18s - but the effort descended into chaos, with stampedes, shortages of supplies, and incidents of violence.
Covid is only one factor in the unrest. Tunisia has had nine governments since the 2011 revolution, many of them short-lived or fractured.
Deep-rooted problems of unemployment and crumbling state infrastructure that were behind the uprising have never been resolved.
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