— -- Authorities have arrested nine people in connection with a gun attack at the Bardo Museum in Tunis that killed 22 people and two alleged attackers, a spokeswoman for the Tunisian presidential office told ABC News.
“Four of the arrests were directly related to the attack, and five others were made under strong suspicion of relation to the attack,” the spokeswoman, Aida Klibi, said of the arrests made Wednesday.
She would not reveal further information on the identity of those arrested.
Meanwhile, searchers found three more people still hiding at the museum today, and authorities in the United States are stepping up security at some of this country's most popular museums, fearful of a follow-on or copy-cat attack.
In New York overnight, extra police were assigned to the city's most popular museums in a direct response to the attack at the museum in Tunisia.
"I'd call this a rather loud wake-up call for major museums around the world," said Peter Herdrich, vice chairman of The Antiquities Coalition, an archaeological advocacy group.
The attack in Tunisia came without warning, and security forces did not arrive in time to prevent the massacre.
Tourists inside the crowded museum in Tunisia's capital city ran for their lives, some shielding their children, as two gunmen approached. Later, they hid inside the galleries beneath priceless antiquities.
Two Spanish tourists and a guard were found still hiding today in the sarcophagus room, a museum official said.
A French tourist said police ordered museum visitors to run, run, run, adding that when they left the museum they saw dead bodies.
Officials this morning said at least 24 died, and 48 more were injured, including tourists from Poland, Germany, Spain and Italy, most of them massacred as they got off a tour bus that brought them to the museum from a cruise ship.
An eyewitness said one of the gunmen actually got on the tour bus and opened fire.
The parliament building next door to the museum was put on lockdown as defiant lawmakers sang the country's national anthem.
Tunisian Prime Minister Habib Essid said two gunmen were killed and police were searching for two or three more who may have been accomplices.
The museum attack came as terror groups call for attacks on soft targets and cultural centers.
"My concern would be that an individual who is becoming radicalized in their basement is watching a video on the Internet of an attack and decides that they want to replicate it," said John Cohen, a former counterterrorism official and an ABC News contributor.
ISIS has made repeated threats against Tunisia, but authorities this morning said they believe another terror group was responsible -- but one that, like ISIS, has no hesitation to attack innocent Western tourists.
One of the two gunmen, Yassine Laabidi, was known to intelligence services but had no formal links to a particular terror group, Essid said on French radio today, according to The Associated Press.
ABC News' Michael S. James, Cho Park, Louise Dewast, Alexander Hosenball, Divya Kumar, Rym Momtaz and Phoebe Natanson contributed to this report.