"The Islamic State (IS) claimed credit for the raid on the Bardo Museum in the Tunisian capital, Tunis, and warned that the attack is the 'first drop of the rain'," US-based SITE Intelligence Group said in a statement.

The statement described Wednesday's attack in Tunisia as a "blessed invasion of one of the dens of infidels and vice in Muslim Tunisia."

"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 read.

Meanwhile, a day after 23 people were killed in an attack at the Bardo Museum in Tunisia's Tunis city, nine people have been arrested so far in connection with the incident, media reports said on Thursday.

The Tunisian Presidency has alleged that four were directly linked to the attack and five had "ties to the cell," BBC reported.

One of two gunman involved in the Bardo museum attack, identified as Yassine Laabidi, was reportedly known to the authorities.

He and his aide Hatem Khachnaoui were killed by the security forces on Wednesday.

Around 23 people were killed as gunmen attacked Bardo Museum in Tunisia's Tunis city on Wednesday.

The deceased included 20 tourists from Japan, Colombia, the UK and other European countries.

The Parliament, which is located close to the museum, had been evacuated after the attack.

The museum is known to have major collection of Roman mosaics and other antiquities of interest from Ancient Greece, Tunisia among others.

Condemning the attack, Indian Prime Minister Narendra Modi tweeted: "Attack in Tunisia is appalling & condemnable. We stand firmly with the people of Tunisia in this hour of grief & pray normalcy returns soon."