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.