TUNIS, Tunisia - Authorities bolstered security across the country Friday amid fears of more attacks after a museum massacre claimed by the Islamic State and carried out by gunmen who apparently trained in Libya.

Security forces were deployed at key sites including the main Mediterranean port in the capital, Tunis, and the headquarters of state radio following a threat against the broadcaster. An Interior Ministry spokesman said police were aware of a specific threat against Radio Tunisia but gave no other details. The full-scale security patrols were reminiscent of the dispatch of troops across France after a series of attacks in Paris by Islamist gunmen in January.

As in France, demonstrators in Tunisia were also voicing their resolve to stand up to terrorism in the country that sparked the Arab Spring revolts across the region four years ago.

In Tunis, hundreds gathered, waving Tunisian flags in a show of solidarity against the attacks at the world-renowned Bardo National Museum. Some held aloft signs reading "Je Suis Bardo," French for "I am Bardo," echoing the defiant phrase "Je Suis Charlie" following the Paris attacks that began at the satirical newspaper Charlie Hebdo.

On Thursday, the Islamic State said that two of its fighters had carried out the museum attack that killed 21 foreign tourists - the latest death reported Friday - in a rampage that raised fears of the jihadist group's growing international footprint.

Rafik Chelli, the Interior Ministry's top security official, said Friday the attackers had slipped out of Tunisia in December and received weapons training in neighboring Libya. Chelli, speaking on the el-Hiwar el-Tounsi TV channel, said authorities did not have further details.

But a friend of one of the slain gunmen said the training was in the eastern Libyan city of Derna, which is partly controlled by groups loyal to the Islamic State.

In an audio recording distributed online, the Islamic State said the gunmen, both Tunisians, struck "citizens of the Crusader countries," according to a translation by the SITE Intelligence Group. The statement marked the first time the Islamic State has claimed an operation in the North African nation.

In Washington, White House spokesman Josh Earnest said Friday there was no clear evidence yet linking the Islamic State to the Tunis attacks.The two militants - who were killed in a shootout at the museum Wednesday - appear to have been radicalized in their home towns in a province bordering Algeria and apparently traveled to Libya for training, according to local media reports and an interview with a friend of one of the militants' families. Their brazen assault has highlighted the danger that the violent jihadist movement poses to this nation, which gave birth to the Arab Spring and is struggling to maintain its democracy.

"I want the Tunisian people to understand that we are in a merciless war against terrorism and that these savage minorities do not frighten us," Tunisian President Beji Caid Essebsi said Thursday.

Tunisian authorities said nine people were arrested in the attack, which killed tourists from countries including Italy, Spain, Britain, Belgium, France, Colombia, and Japan.

Two cruise ships whose passengers were among those killed, reached Spain Friday.

Giovana Gonzalez of Miami had just left a restroom at the end of a museum tour when the attackers "started shooting everybody," the Associated Press reported. "Everyone ran in different directions," she told reporters after disembarking from her cruise ship in Barcelona. She and her husband were on a cruise to celebrate their 25th anniversary.

In Palma, Spanish cruise ship passenger Catalina Llinas told reporters she and her husband visited the Roman ruins of Carthage instead of joining the trip to the museum. "It could have been us," she said.