An al Qaeda-linked group said it killed nearly 300 people in Saturday's devastating attack in north-central Burkina Faso, but said it targeted militia members linked to the army, not civilians, the U.S. consultancy Site Intelligence Group reported.

The attack outside the town of Barsalogho was one of the deadliest in nearly a decade of Islamist violence in the West African country.

A group of victims' relatives said at least 400 were killed when jihadists opened fire on civilians digging defensive trenches on orders of the military.

Al Qaeda affiliate Jama'a Nusrat ul-Islam wa al-Muslimin said soldiers and militia members were excavating the trenches when it attacked.

"Those who were eliminated in this attack are nothing but militias affiliated with the Burkinabe army ... not as they lied and said that they were civilians," JNIM said in a communique translated by Site on Thursday.

Several videos apparently filmed by the militants and released on social media showed dozens of bodies in trenches, most of them in civilian clothing.

The bloodshed highlights the danger of the authorities' growing reliance on civilians as they struggle to combat jihadist groups that have destabilised swathes of the Sahel region since an insurgency took root in neighbouring Mali in 2012.

"Civilians are playing a significant role in the conflict," said Ryan Cummings, director of analysis at Africa-focused risk-management company Signal Risk, referring to their recruitment into militia or in fortifying towns, as they appear to have been doing in Barsalogho.

"But civilians that are assisting the military are seen as collaborators. This has made them targets of attacks," he said.

Burkina Faso's ruling junta has not said how many people were killed, but said civilians, soldiers and volunteer army auxiliaries known as VDPs were among the victims.

State television reported that the attackers struck while Barsalogho locals were engaged in unspecified community work.

On Wednesday, citizen advocacy group Collectif Justice pour Barsalogho said the authorities were negligent for using the military to force the community to build trenches, "which turned out to be mass graves."

"Our parents were led to the slaughter," it said in a statement.

Frustrations over worsening violence led to two coups in Burkina Faso in 2022, but the new authorities have failed to stem the bloodshed. Over 6,500 civilians have been killed since the start of 2020, the nongovernmental organisation Armed Conflict Location and Event Data showed in July. More than half died under the current government.