Bamako - Gunmen attacked a town in western Mali near the border with neighbouring Mauritania before dawn on Saturday, a town resident and a senior military source said.It was not immediately clear who was behind the attack, which took place a week after a Tuareg-led northern rebel alliance signed a peace deal with the government aimed at ending their uprising and allowing the authorities to focus on combatting Islamist militants.Gunfire erupted at around 05:00 in the town of Nara, around 30km south of border with Mauritania."There was an exchange of gunfire with the [Malian army]. The attack was repelled. The army is patrolling in the town to look for them," army spokesperson Colonel Souleymane Maiga said.There was no immediate information on casualties, he added.A resident said that gunfire was still being heard several hours after the clashes began."We are in our houses. No one is going out. All the houses are closed up. The fighting is going on now," one town resident said, asking not to be named.A French-led military campaign in early 2013 liberated northern Mali from al Qaeda-linked Islamist rebels, who seized control of the area after the Tuareg uprising led to a military coup that plunged Mali into chaos.Insecurity persists however, and though the violence, often blamed on the remnants of Islamist groups, is generally focused in the desert north, attacks have in recent months crept further south.Dozens of suspected Islamist militants attacked a police base near Mali's southern border with Ivory Coast earlier this month.