Isis claims responsibility for Tunisia museum attack and warns deadly shooting is 'just first drop of the rain'

Statement warns: 'Wait for glad tidings of what will harm you'

Members of the Tunisian security services take up a position outside the National Bardo Museum, near the country's parliament after gunmen reportedly took hostages at Tunisia museum in Tunis,Tunisia on 18 March 2015

(EPA/MOHAMED MESSARA)

Isis has claimed responsibility for the attack on a museum in the capital of Tunisia, which claimed the lives of 23 people, saying it was only the “first drop of the rain”.

Gunmen burst from a vehicle and began firing at buses transporting tourists to the Bardo Museum in Tunis on Wednesday, killing British cruise passenger Sally Adey, 57.

The atrocity was the worst at a tourist site in Tunisia in more than a decade and Isis' most deadly assault on Westerners since its separation from al-Qaeda last year.

Amedy Coulibaly, who killed five people in the wake of the Charlie Hebdo massacre, was inspired by the group, as was the Sydney siege gunman and the Canada Parliament shootings.

A statement released by one of the militant group's official channels described the attack as a "blessed invasion of one of the dens of infidels and vice in Muslim Tunisia".

The statement warned the attack is the “first drop of the rain”, according to the US monitoring group SITE.

"Wait for the glad tidings of what will harm you, impure ones, for what you have seen today is the first drop of the rain," it said.

People make their escape from the Bardo Museum in Tunis during an attack by men armed with assault rifles

(Getty Images)

The statement, which was circulated by Twitter account affiliated with the group, said the deadly attack was committed by "two knights of the caliphate" and named the gunmen as Abu Anas al-Tunisi and Abu Zakariyya al-Tunisi.

Tunisia has arrested nine people in connection with assault. The Tunisian Prime Minister admitted one of the gunmen was known to intelligence services but but "not for anything very special".

The pair had trained at a jihadist camp in Libya, the government said on Thursday.

Interior minister official Rafik Chelli said the two men had been recruited at mosques in Tunisia and travelled to Libya in September.

A cruise company 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.

Ms Adey was also a passenger of MSC Splendida. Family friend Julia Holden described her as “a much-loved daughter, wife and mother”.

According to Adey's profile on website Beemee, she was a lawyer with children in university. She listed her interests as “family, cooking, flowers, history, watching sport with my husband — golf, rugby, cricket, motor racing and weekends away with friends.”

Up to 3,000 people have left Tunisia to fight with Isis in territories under its control in Syria and Iraq, making up a significant proportion of their foreign fighters.