TUNIS (Reuters) - Islamist militants attacked a checkpoint in a town in southwest Tunisia early on Sunday, killing a policeman and wounding three others, security officials said.

Two militants were also killed in an exchange of fire during the attack in Kebili, which lies on the edge of Tunisia’s southern desert region, said the officials, speaking on condition of anonymity.

The attackers opened fire on a police patrol that had set up a checkpoint at a roundabout in the town, one security official said.

Security forces were combing the area to search for militants who may have escaped following the attack, a second official said.

Tunisia has been trying to tackle a jihadist threat after suffering major attacks by Islamist militants in 2015 and early 2016, including deadly assaults on tourists at a museum in Tunis and on a beach in Sousse.

Militants occasionally target patrols and checkpoints, but attacks in towns and cities are rare. Sunday’s was the first in an urban area since a bomb attack against a bus carrying presidential guards in Tunis in November 2015.