Tunisia was under a state of emergency Wednesday after the bombing of a presidential guard bus killed at least 13 people, the latest attack in a country plagued by Islamist violence.
President Beji Caid Essebsi and other members of the National Security Council were meeting to discuss crisis measures following the blast on Tuesday in the heart of Tunis.
A 9:00 pm to 5:00 am curfew has been imposed in the capital following the attack, along with a new nationwide state of emergency, which had been lifted less than two months previously.
There was no immediate claim of responsibility for the bombing in a busy area in the heart of Tunis, a few hundred metres (yards) from the interior ministry, which came as the 26th Carthage Film Festival was in full swing.
The ISIS group has previously staged attacks in the North African country, often seen as a rare success story of the Arab Spring after its 2011 overthrow of longtime dictator Zine El Abidine Ben Ali.
Twelve presidential guards were killed and 20 other people were wounded in Tuesday's blast, including four civilians, according to a preliminary toll from the health ministry.
The remains of a 13th person found at the scene have not yet been identified, officials said.
"It could be that this is a terrorist," Health Minister Said Aidi told national television.
According to unconfirmed reports in Tunisian media, the blast was caused by a man wearing an explosives belt.
Some presidential guards expressed concern that not enough was being done to protect them from attacks.
"For years this place has been our gathering point but they didn't think to change it although we are the first to be targeted," one guard said of the site of the bombing.
The transport ministry announced following the blast that security would be reinforced in the country's ports and only passengers would be allowed to enter Tunis's international airport.
A psychological unit was set up for the victims' families.
Tunisia has been plagued by Islamist violence since the 2011 revolution and dozens of members of the security forces have been killed.
Two attacks this year claimed by the ISIS group targeted foreigners -- at the National Bardo Museum in March, killing 21 tourists and a policeman, and at a resort hotel in Sousse in June, killing 38 tourists.
A year ago, a bus carrying troops was attacked by two armed men in northwest Tunisia, according to the defence ministry. Five soldiers were killed.
In July 2014, 15 soldiers were killed in the Mount Chaambi region near the Algerian border, in the worst such attack in the army's history.
The United States condemned the latest attack and offered to help the Tunisian authorities with their investigation.
US Secretary of State John Kerry "was proud to stand with Tunisian leaders earlier this month in Tunis and reaffirm our countries' extensive economic, governance, and security cooperation", a spokesman for his department said.
Tunisia's press called Wednesday for national unity and resistance.
"United against barbarism" declared Le Quotidien. "Tunisia will not bend," said Le Temps, while Al Maghreb called for "a new philosophy and special measures" to fight terrorism.
The attack came after a militant group on Sunday claimed the beheading of a young Tunisian shepherd on behalf of ISIS, accusing him of having informed the army about their movements in the central province of Sidi Bouzid.
The killing of 16-year-old Mabrouk Soltani on November 13 sparked anger in Tunisia. His killers ordered a 14-year-old who was working with him to bring the victim's head wrapped in plastic to his family.
The authorities regularly announce the arrests of suspected militants.
Seven women were recently detained for engaging in pro-ISIS propaganda, while 20 people were arrested on suspicion of planning attacks on hotels and security facilities.
Thousands of Tunisians are fighting in neighbouring Libya, as well as in Iraq and Syria on the side of militants.