Tunisia says it's closing its border with Libya, a hotbed of Islamist unrest, a day after a deadly suicide bombing claimed by the Islamic State group.
No reason was given, but the interior ministry said earlier the explosive used in the attack that killed 12 presidential guards was the same used to make explosive belts illegally brought from Libya and seized last year.
The National Security Council, headed by President Beji Caid Essebsi, decided to close the frontier from midnight with "reinforced surveillance of maritime borders and in airports", a statement said.
It also decided to "step up operations to block (internet) sites linked to terrorism".
And authorities would "take urgent measures regarding people returning from hotbeds of conflict, in line with the antiterrorist law," the statement added, without elaborating.
Earlier, the transport ministry said security would be reinforced at ports and only passengers would be allowed to enter Tunis's international airport.
Thousands of Tunisians have travelled to Libya, as well as to Iraq and Syria, to fight alongside Islamic extremists, the authorities say.
The council also announced the government would recruit more interior ministry agents and soldiers next year.
IS said a Tunisian, Abou Abdallah al-Tounissi, had boarded a bus wearing an explosives belt only a few hundred metres from the interior ministry as it picked up guards on their way to work Tuesday.
In addition to the 12 killed, another 20 people were wounded, the health ministry said.
IS said 20 people had died.
After the blast Essebsi ordered a curfew for Tunis and a nationwide state of emergency, less than two months after a previous one had been lifted.
That was imposed in June after an IS gunman massacred 38 foreign tourists at the Mediterranean resort of Sousse.
In March, two IS jihadists stormed the National Bardo Museum in Tunis, killing 21 tourists and a policeman.
And just days ago, a jihadist group claimed the beheading of a young Tunisian shepherd on behalf of IS, accusing him of having informed the army about their movements.