Four Tunisian police were killed when gunmen opened fire on the interior minister's family home in western Kasserine region, an official with the ministry said today.

The minister was not at home during the attack, ministry spokesman Mohammed Ali Laroui said. No group immediately claimed responsibility, but Tunisian forces are engaged in a crackdown on the hardline Islamist group Ansar al Sharia.

Laroui said another policeman was wounded when the gunmen opened fire and then fled.

Tunisia's armed forces this year launched a major assault on the Chaambi mountains in the western region close to the frontier with Algeria where a Islamist militants have taken refuge.

Ansar al Sharia, listed in January as a foreign terrorist organisation by the United States, was one of the hardline Islamist movements to emerge after Tunisia's 2011 "Arab Spring" revolt ousted autocrat Zine El-Abidine Ben Ali.

The North African state's political transition has advanced since the uprising. But Tunisian authorities are worried about spillover from neighbouring Libya where turmoil has allowed Islamist militants to gain a foothold.