Tunisian police have arrested a group of Islamist militants who accidentally exploded a bomb they were manufacturing as part of a planned attack on the country's commercial city of Sfax, the government said on Sunday.

The interior ministry said police had arrested eight suspected members of the militant group Ansar al-Sharia late on Saturday as part of a raid in Sfax, a Mediterranean port city around 170 miles (270 km) southeast of the capital Tunis.

Two of those arrested were wounded in the bomb blast while handling the explosive, the ministry said in a statement.

Ansar al Sharia, listed as a foreign terrorist organisation by the United States, was one of the most hardline movements calling for an Islamic state to emerge since Tunisia's 2011 uprising ousted autocrat Zine El-Abidine Ben Ali.

With an economy heavily reliant on foreign tourism, Tunisia has been cracking down on Islamist militants that it views as a key challenge on its path to full democracy.

One of the Arab world's most secular states, Tunisia has adopted a new constitution and a caretaker government has taken over as a way to ease tensions between a leading Islamist party and secular opponents until elections due later this year.