Thirteen paramilitary police were killed Saturday in a fresh attack in Niger's restive southwest, just weeks after a deadly ambush on a joint US-Niger patrol.
The region which borders Mali has faced a series of recent jihadist incursions.
Saturday's dawn raid happened in the town of Ayorou in the Tillaberi region, 200 kilometres (124 miles) northwest of the capital Niamey.
"The Ayorou gendarmerie was the subject of a terrorist attack perpetrated by unidentified armed elements in vehicles and on motorcycles," said defence ministry spokesman Colonel Amadou Samba Gagara on public television.
"The provisional assessment is as follows: 13 dead soldiers and five others injured."
A security source said the attackers arrived in five vehicles and fled when military reinforcements arrived. Villagers saw them leave carrying bodies.
On October 4, four US and four Niger soldiers were killed in what Niamey called a "terrorist attack" that confirmed the little-known presence of US troops in the turbulent area as part of a counter-terrorism operation.
The source on Saturday revealed a village elder had been arrested in connection with that attack.
"The chief of Tongo Tongo (village) was basically arrested after the October 4 attack for 'complicity' with the attackers," the security source told AFP.
He said the chief "delayed a meeting for a few minutes" as local elders gathered to meet US soldiers which had aided the ambush by giving the assailants an opportunity to carry out their attack.
Karimou Soumana, a Tillaberi regional lawmaker, confirmed the arrest to parliament and said the chief was being urged to reveal the attackers' whereabouts.
Niamey and Washington had both earlier indicated they believed there was "complicity" between some local officials and jihadist fighters.
The Tallaberi region has become increasingly unstable due to numerous deadly attacks attributed to jihadist groups who regularly target army positions and refugee camps.
In mid-May unidentified assailants attacked the same Ayorou gendarmerie without causing any casualties.
On Friday, parliament agreed a three-month extension of the state of emergency in western Niger because of the "continuing threat" of armed groups.
The UN said this week it has documented "at least 46 attacks" in Niger since February 2016.
As well as trouble along its Mali border, the country is also facing incursions from the Nigerian Islamist group Boko Haram along its southeastern border with Nigeria.
In June, Niger set up an operation of 245 men to fight against jihadists but has not yet reported on its progress.
Malian foreign affairs minister Abdoulaye Diop stressed in front of the UN Security Council in New York this month the urgent need to help a new international security force get off the ground.
The so-called "G5 Sahel" coalition of Burkina Faso, Chad, Mali, Mauritania and Niger -- countries that have been badly hit by jihadist attacks but whose military resources are thin -- have pledged to fight terror but face funding problems.
Mali has become a particularly volatile country since 2012 when jihadist groups captured the entire north of the country.
Entire zones still escape the control of Malian and foreign forces, despite a military intervention by France in 2013.