France, June 11 -- Rainy season had already begun in 2017 when thousands of artisanal miners working around Namanhumbir, near Montepuez in the northern Cabo Delgado province of Mozambique, saw security forces approaching.

Many were arrested for what the authorities called illegal mining. Most of the miners, known locally as garimpeiros, came from outside the region.

Some returned to their home districts or crossed into neighbouring southern Tanzania. Others joined a little-known armed group that was gaining strength in northern Mozambique - known locally as Al-Shabab and linked to the Islamic State group (although with no connection to the Somali militant group of the same name).

"From then on, it was war," one miner recalled in a 2021...