Spokesman Khalifa Chibani told AFP the National Guard had received information concerning "two male suspects" in the southern Ben Guerdane region.

They tracked them down in the Magroun area, a desert zone near a nature reserve, and tried to arrest them but "one of them blew himself up," he said.

Chibani said both suspects wore explosive vests, and had currency from chaos-wracked Libya, grenades and ammunition. "It is probable that they were planning to go to Libya," he told AFP.

One of the suspects, he said, was armed with a Kalashnikov assault rifle and had opened fire on the police.

After an exchange of fire, security forces "shot dead the second terrorist", the interior ministry said later, adding that the National Guard and the army were searching the area.

The identity of the two suspects was not immediately clear.

Chibani said an investigation had been opened and would determine if the first suspect who blew himself up had activated his explosives vest or if it blew up in the exchange of fire with the security forces.

Since its 2011 revolution, Tunisia has faced a jihadist insurgency responsible for the deaths of dozens of soldiers, police, civilians and foreign tourists.

Tunisia has been under a state of emergency since November 2015, when a suicide bombing in Tunis claimed by the Islamic State jihadist group killed 12 presidential guards.

Monday's incident comes after a series of deadly operations in 2015 and two years after an IS offensive into the town of Ben Guerdane.

On March 7, 2016, jihadists launched brazen attacks on the town that killed 13 members of the security forces and seven civilians and also left 55 fighters dead.

Prime Minister Youssef Chahed this month marked the anniversary of the Ben Guerdane attacks and said he wanted to "consecrate March 7 as a national day of victory against terrorism" and Ben Guerdane as "the town of victory against terrorism".

Thousands of Tunisians have joined jihadist groups fighting in Iraq, Syria and neighbouring Libya.