Tunis, March 19  The Islamic State (IS) terrorist group is believed to be behind the attack on a museum in Tunisia’s parliament complex which killed 23 people, including 20 foreign tourists, media reports said on Thursday.

The IS said in an audio message that the attack on the Bardo museum in Tunis was carried out by “two knights of the caliphate” and named them as Abu-Zakariya al-Tunisi and Abu-Anas al-Tunisi, according to a BBC report.

The statement was published on Twitter accounts known to be reliable primary sources of IS propaganda, the report added.

At least 19 people, including 17 foreign tourists, were killed when two “terrorists” disguised as soldiers attacked the museum through the parliament building.

The attackers were killed later by the security forces, Tunisian Prime Minister Habib Essid said. An earlier report said the two attackers “could have been assisted by two or three other operatives”.

One of gunmen involved in the attack, named by Tunisian officials as Yassine Laabidi, was known to the authorities, the BBC report said, adding that Laabidi and his accomplice, named as Hatem Khachnaoui, were killed as security forces stormed the museum.

In another development, the Tunisian presidency said nine people were arrested in connection to Wednesday’s attack, according to BBC.

It said four were directly linked to the attack and five had “ties to the cell”.

The army will be deployed to major cities, the presidency added.

It said Tunisia was facing “exceptional circumstances”, and “terrorist operations have now moved from the mountains to the cities”.

Tourists from Japan, Italy, Colombia, Australia, France and Poland, and two Tunisians, one of them a police officer, were killed in the attack.

Prime Minister Habib Essid said around 100 tourists were inside the museum when it was attacked.

A Spanish couple presumed dead in the attack were, however, found alive, Spanish news agency Efe reported citing an official from the MSC shipping company in which the couple had travelled to Tunisia.

The Indian leadership joined the chorus of world leaders condemning the deadly attack.

Prime Minister Narendra Modi was one of the first to condemn the attack and express condolence for the victims.

President Pranab Mukherjee on Thursday “strongly condemned” the “senseless” attack.

UN Secretary-General Ban ki-Moon condemned the attack and expressed “his solidarity with the Tunisian people and the Tunisian authorities”.

Bardo Museum is the biggest Tunisian museum and a major tourist attraction.

The museum is housed in a 19th century palace and describes itself as “a jewel of Tunisian heritage”. Its exhibits Tunisian art, culture and history.

The museum is significant for its location — in the heart of Tunis and physically linked to parliament.

The fact that there was a significant number of foreign tourists at the museum during the attack was not surprising, given the museum’s prominence and the fact that at least two cruise ships, including the MSC Splendida and Costa Fascinosa, were docked in Tunis at the time.