TUNIS — Four Tunisian police were killed on Wednesday when a suspected extremist militant detonated his suicide-bomb belt during a raid in the southern town of Tataouine, part of an operation aimed at preventing militant attacks in Tunis, authorities said.

Another militant was shot dead during the raid. Earlier, two more were killed in a raid in Ettadamen, a suburb of Tunis, the interior ministry said.

Security forces are engaged in a crackdown after four major attacks in the last year by Islamist militants. The assaults on a Tunis museum, a beach resort and a border town near Libya have badly damaged the vital tourism industry.

Sixteen suspects were also arrested in the Tunis raid, and rifles, grenades and ammunition were captured.

“The terrorists came from different parts of the country and gathered in the capital, particularly Ettadhamoun, to prepare synchronized attacks,” a statement by security forces said.

Authorities say more than 4,000 Tunisians have left to fight for militant groups in Iraq and Syria, and some have returned to training camps run by ISIS across the border in neighboring Libya.