By Tarek Amara
TUNIS, March 21 (Reuters) - Tunisian authorities have arrested more than 20 suspected militants following the Bardo museum attack when gunmen killed foreign tourists, leading to a nationwide security crackdown, the government said on Saturday.
Hundreds of Tunisians gathered for a mass in the cathedral in Tunis on Saturday, lighting candles to remember the victims - 20 foreign tourists and three Tunisians - in a ceremony attended by government ministers.
Outside, there was a heavy police presence along the capital's central Habib Bourguiba boulevard. But the city was calm with a music festival planning to continue with its concerts in the city center.
Wednesday's assault - the most deadly attack involving foreigners in Tunisia since a 2002 suicide bombing in Djerba - came at a fragile moment for a country just emerging to full democracy after a popular uprising four years ago.
The government said the two gunmen had trained in jihadi camps in Libya before the attack at the museum inside the heavily secured Tunisian parliament compound. Japanese, French, Polish, Italian and Colombian visitors were among the victims.
Authorities have arrested more than 20 suspected militants, including 10 believed to be directly involved in the Bardo attack, Interior Ministry spokesman Mohamed Ali Aroui said.
"There is a large-scale campaign against the extremists," he said.
The interior ministry also released a photograph of another suspect and asked Tunisians to help with information.
The government plans to deploy the army to major cities to improve security following the shootings.
Islamic State militants have claimed responsibility for the attack, but social media accounts tied to an Al Qaeda-affiliated group in Tunisia have also published details purported to be about the operation.
Whoever was responsible, the Bardo attack illustrates how Islamist militants are turning their attention to North Africa, especially in neighboring Libya where two rival governments battle for control allowing Islamic State to gain a foothold.
The United States is increasingly worried about the growing presence of Islamic State militants in Libya.
U.S. officials said that because of its strategic position, Libya has become a springboard for would-be fighters from across North Africa wanting to link up with Islamic State. They could travel from there to Syria for frontline experience.
Four years after a popular revolt toppled autocrat Zine El-Abidine Ben Ali, Tunisia has completed its transition to democracy with free elections, a new constitution and compromise politics between secular and Islamist parties.
But the attack threatens to hit the economy of a country that is heavily reliant on foreign tourists to its beach resorts and desert treks. Authorities have tightened security at hotels and tourist spots.
"This attack will have an impact, no doubt. But so far we have only had a small number of cancellations," Tourism Minister Salma Loumi told Reuters. "On the contrary, we are seeing support from Western countries and travel agencies." (Writing by Pat Markey; Editing by Pravin Char and Stephen Powell)