"On Monday July 22, a unit of the defence and security forces exchanged fire with armed terrorist groups along the Bankilare-Tera route near the village of Foneko", it said in a communique read on state television, announcing a "preliminary toll" of 15 dead.

The ministry also said three soldiers were missing with 16 injured and hospitalised, adding that 21 "terrorists" had been killed in the clashes in the western region of Tillaberi.

The ministry went on to say the "prompt intervention of reinforcements from Tera" had forced the armed groups to retreat to the north.

The attack came almost exactly a year after a military coup which the army justified by the country's deteriorating security situation.

Twelve months on, armed groups notably from Islamic State and others loyal to Al-Qaeda, have continued to carry out attacks in the Tillaberi region, with bloody clashes over recent weeks leaving dozens dead on both sides.

Despite a large-scale rollout of troops and a junta promise to quadruple military numbers by 2030, civilians have also not been spared by the unrest -- though victim tolls remain imprecise amid scant independent data.

Tera is an intersection point for the thousands of cargo trucks arriving each month from the port of Lome, in Togo, via northern Burkina Faso. The lorries are escorted by troops from both neighbouring states.

Four weeks ago, 20 soldiers and one civilian were killed in the same region in an attack by armed groups. The army said it had killed "more than 100 terrorists" in response.

Earlier this month seven civilians were killed in the nearby village of Dosso Kouregou.

Niger is also having to contend with violence in its southeast from Boko Haram and Islamic State's West African offshoot.

Military leader General Abdourahamane Tiani meanwhile has declared Friday an official holiday to mark a year since the overthrow of elected President Mohamed Bazoum.

Since taking over, the junta has totally reset its international partnerships, asking former colonial power France late last year to withdraw its troops that had been combatting jihadist groups in the Sahel nation.

By mid-September, a US contingent is also due to pull out of an important drone base at Agadez in the north.

Instead, Niamey has been fostering closer links to Iran, Turkey and Russia.

Russia notably sent military instructors to Niger in April and May.

On a regional level, Niger has engaged in rapprochement with Burkina Faso and Mali, likewise ruled by military juntas after recent coups.