Washington: The White House has said that investigators have been unable to determine if the Islamic State (IS) terrorist organisation was behind the attack last weekend on a Texas exhibit of cartoons of the Prophet Mohammad, despite the claim of responsibility IS issued via its Internet radio station.

\"Too early to tell,\" was White House press secretary Josh Earnest\'s response on Tuesday when asked whether the two assailants -- who died in the attack -- had any connection to IS, reports Efe.

The two gunmen, who shot and wounded a security guard before they were fatally shot by police, were Arizona residents, and one of them had been investigated in the past for links to terrorism.

\"The thing that we can say definitively, because of the quick, professional, brave work of local law enforcement forces, is an attempted terrorist act was foiled,\" Earnest said at his daily press briefing.

In addition, the spokesperson said that the government of Barack Obama remains on the alert for attempts by the IS and other extremists to \"radicalise\" and recruit individuals in the US.

The attack was staged on Sunday at the Curtis Culwell Center in Garland, a Dallas suburb, and the two gunmen were identified as Elton Simpson, 30, and Nadir Soofi, 34.

Simpson was known to the FBI, given that in 2011 he was sentenced to three years on parole for lying about his plans to travel to Somalia to join a terrorists group.

In an information bulletin issued by online radio station al-Bayan, the IS took responsibility for the attack, the first that the terrorists claim to have carried out on US soil.

\"Two of the soldiers of the caliphate executed an attack on an art exhibit in Garland, Texas, and this exhibit was portraying negative pictures of the Prophet Mohammad,\" an announcer said.

The Garland exhibition was being sponsored by the New York-based American Freedom Defence Initiative, which offered a $10,000 prize for the winning cartoon.

In January, 12 people were murdered in Paris at the offices of French satirical weekly magazine Charlie Hebdo, after it published cartoons of the prophet, an attack that was claimed by Al Qaeda in the Arabian Peninsula.

Many Muslims regard depictions of the prophet as blasphemous.

Washington can\'t confirm IS was behind Texas shooting