A tourist is helped to a vehicle after an attack by gunmen on Tunisia's national museum in Tunis, March 18, 2015. [Photo/Agencies]

Confronted with a poor economy, young Tunisians have disproportionately gone abroad to fight with extremist groups in Libya, Syria and Iraq, including some affiliated with the Islamic State. Upon their return home, some may have decided to carry out attacks on their own.

Tunisian authorities have estimated that of the 3,000 young people who left the country to fight with radical groups, about 500 have returned.

"It could have been people who fought with the Islamic State or were inspired by it," said Raffaello Pantucci, director of International Security Studies at the Royal United Services Institute, a British think tank. "Some guys may have come back, not liked what the government is doing, and attacked the tourist industry to hurt the economy - a classic move."

Tunisia is particularly vulnerable to such attacks because its economy has struggled since the country became the birthplace of the Arab Spring by overthrowing its dictator in 2011.

At a news conference Thursday, Prime Minister Habib Essid announced new security measures around the country, including a crackdown on websites seen as promoting terrorism.

The deaths of so many foreigners will damage Tunisia's tourism industry, which draws thousands of foreigners to its Mediterranean beaches, desert oases and ancient Roman ruins. The industry had just started to recover after years of decline.

Two cruise ships that had 17 passengers among the dead quickly left the port of Tunis early Thursday, citing safety concerns, and the vessels' operators suspended visits to the country.

Culture Minister Latifa Lakhdar gave a news conference at the museum, where blood still stained the floor amid the Roman-era mosaics.

"They are targeting knowledge. They are targeting science. They are targeting reason. They are targeting history. They are targeting memory, because all these things mean nothing in their eyes," she told reporters.