The Islamic State (ISIS/ISIL) has claimed responsibility for an explosion that struck a bus carrying Tunisia’s presidential guard in the country’s capital of Tunis, killing at least 13 people and injuring more than a dozen others.

ISIS, in a message posed on social media, said that the terrorist attack on Tuesday was carried out by a suicide bomber, BBC reports.

Tunisia’s interior ministry revealed that a backpack or belt containing 10 kg of military explosives was used.

Tuesday’s explosion marks the third high-profile attack in Tunisia this year for which ISIS has claimed responsibility. ISIS assumed responsibility for staging two attacks in Tunisia earlier this year that killed nearly 60 people and devastated the country’s tourism industry.

The White House condemned the recent attack “in the strongest terms.”

Tunisia’s President Beji Caid Essebsi, who was not onboard the bus at the time of the attack, has “declared a 30-day state of emergency across the country and imposed an overnight curfew on the Tunis region,” reports The Associated Press (AP).

Tunisia has reportedly closed its border with Libya, where ISIS has a strong presence, for 15 days.

On Wednesday morning, the Tunisian president convened an emergency meeting of his security council.

Tunisia is at “war against terrorism,” Essebsi said on national television, urging international cooperation against terrorists who have carried out several deadly attacks in recent weeks.

“I want to reassure the Tunisian people that we will vanquish terrorism,” added the president.

The attack reportedly took place at a bus stop located on a tree-lined avenue in the heart of Tunis where the presidential guard picks up and drops off its staff.

A BBC correspondent noted that “it is still not clear whether the bomber boarded the bus reserved for the presidential guard, or simply got close enough to cause the deadly impact.”

The blast “is a new blow to a country that is seen as a model for the region but has struggled against Islamic extremist violence,” notes AP.

Walid Louguini, a spokesmen for Tunisia’s Interior Ministry, told AP that at least 16 people were wounded in the attack.

Bassem Trifi, a human rights lawyer who witnessed the attack, said the blast struck the driver’s side of the bus, describing the incident as a “catastrophic spectacle.”

“I saw at least five corpses on the ground,” he told the AP. “This was not an ordinary explosion.”

Days prior to the attack, Tunisian authorities increased the security level in the capital and deployed security forces in unusually large numbers, reports AP, adding that “the French Embassy is this former French territory was also put under high protection in recent days, after extremist attacks in Paris killed 130.”

“Earlier this month, Tunisian authorities announced the dismantling of a cell that it said had planned attacks at police stations and hotels in the seaside city of Sousse, about 150 kilometers (95 miles) southeast of Tunis,” also reports AP. “Sousse was one of the targets of attacks earlier this year.”

Analysts believe that Tunisia provides the biggest contingent of foreign fighters overseas, with authorities estimating that at least 3,000 Tunisians are fighting in Iraq and Syria, notes BBC.

Tunisians are also believed to be fighting alongside jihadists in neighboring Libya.