After Islamic State took the lives of 20 foreign tourists in an attack on a museum, Tunisia arrested nine people and pledged to deploy the army to major cities. The terror out wing described the attack as “the first drop of the rain”.

Officials have not authenticated the militants' claim of responsibility, but said they had identified the two gunmen shot dead by security forces after opening fire on tourist buses visiting the Bardo museum inside the capital's heavily guarded parliament compound on Wednesday.

Among the corpses are Japanese, Italian, Spanish and British visitors, as well as three Tunisians. Cruise liner MSC Cruises said 12 of its passengers, including Colombians, French and a Belgian, were among the dead, while a Spanish couple was found alive on Thursday after hiding all night in the museum.

This was the nation’s most deadly attack from the past 13 years, which is heavily reliant on foreign tourists to its beach resorts and desert treks.

Islamic State is active in Tunisia's chaotic neighbour Libya, praised the two attackers in an audio recording in Arabic, calling them "knights of the Islamic State" armed with machine guns and bombs.

Tunisians make up the one of the largest contingent of foreign fighters in Syria, Iraq and Libya, and their homeland's young democracy, which has cracked down on militancy at home, was a clear potential target.

"We tell the apostates who sit on the chest of Muslim Tunisia: Wait for the glad tidings of what will harm you, o impure ones, for what you have seen today is the first drop of the rain," read the Islamic State audio.

The two dead militants were identified as Tunisians, Hatem al-Khashnawi and Yassin al-Abidi. Two local newspapers claimed that Abidi had spent time in Iraq and Libya, but officials did not confirm that.

Tunisia's Prime Minister Habib Essid said Abidi had been under surveillance but "not for anything very special".

"We have identified them, it is indeed these two terrorists," the premier told French RTL radio earlier on Thursday. "Their affiliation is not clear at the moment."

Authorities said they had arrested four people directly linked to the attack and detained five other suspects. A security source said two family members of one of the gunmen were among those held. "We arrested the father and the sister of the terrorist Hatem Al-Khashnawi in the their home in Sbiba City," the source told media.

- Manohar