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Christophe Ena, Associated Press
Police officers guard the entrance of the National Bardo Museum a day after gunmen opened fire killing scores of people in Tunis, Thursday, March 19, 2015. One of the gunmen who killed tourists and others at a prominent Tunisian museum was known to intelligence services, but no formal links to a particular extremist group have been established, the prime minister said Thursday.

TUNIS, Tunisia — Tunisian security forces arrested nine people linked to the deadly attack on the National Bardo Museum that left 23 dead, scores wounded and threatened the country's fledgling democracy and struggling tourism industry, the president's office said Thursday.

The statement said five of those arrested were directly connected to the attack by two gunmen while the other four were arrested in the center of the country and part of a cell supporting those involved.

One of the gunmen was known to intelligence services, but no formal links to a particular extremist group have been established, the prime minister said Thursday.

The attack was the worst at a tourist site in Tunisia in years, and a leading cruise line announced it is now canceling its Tunisian stops.

Associated Press reporters Mari Yamaguchi in Tokyo, Nicole Winfield in Rome, Jeff Schaeffer in Tunis, Monika Scislowska in Warsaw, Harold Heckle in Madrid and Lori Hinnant in Paris contributed to this report.