Malian military authorities say at least four soldiers have been killed in a gun attack and landmine explosion in the West African country’s northeastern region.

An army officer, speaking on condition of anonymity, said a soldier was driving a military vehicle on the outskirts of the ancient city of Timbuktu, roughly 1,000 kilometers (621 miles) north of the capital, Bamako, on Thursday morning, when an armed man opened fire and shot him dead.

The officer added that a manhunt is underway to arrest the assailant.

Separately, three other troops died in a bomb explosion that destroyed their vehicle near the city of Gao, located 320 kilometers (200 miles) southeast of Timbuktu.

Army spokesman, Colonel Souleymane Maiga, said the incident took place 37 kilometers (22 miles) southwest of Gao, when the vehicle at the head of the army convoy struck a buried explosive device.

Mali has been witnessing violence linked to militant activity in its northern regions since 2012. The area remains vulnerable to attacks despite a military operation led by France in 2013, which came after the UN Security Council passed a resolution on the deployment of the UN Multidimensional Integrated Stabilization Mission in Mali (MINUSMA).

Last June, Tuareg separatists, who have launched a number of uprisings since the 1960s, signed a peace deal with the Malian government.

The peace agreement, brokered by Algeria, raised hopes of finally ending years of unrest in the country, however its implementation has proven challenging.