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 suicide 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.
According to Reuters, Tunisian authorities also said a suicide bomber wearing a vest packed with plastic explosive blew up a presidential guard bus a day earlier, killing at least 12 troops in an attack claimed by ISIS.
“This attack is an evolution in the behavior of the terrorists, this time they attacked a symbol of the state and in the heart of the capital,” Prime Minister Habib Essid told reporters after an emergency security meeting.
ISIS, whose insurgents control large parts of Iraq and Syria and are also active in Libya to Tunisia’s east, claimed responsibility Wednesday for the Tunis attack, according to an official statement.
It included a photograph of a man, wearing a headscarf, a white robe and bomb vest, who it said was the bomber and named him as Abu Abdyllah Tounsi. The name suggests he was Tunisian himself.
“The Tyrants of Tunisia must know there is no safety for them. We will not stop until the laws of Allah are applied to Tunisia,” the statement said.