What you need to know:
- Thousands of civilians and soldiers have died in violence across the Sahel which began when armed Islamists revolted in northern Mali in 2012.
- France has some 4,500 troops in the region and the G5 Sahel force has a projected total of 5,000.
- The jihadists have exploited ethnic divisions and a feeling of abandonment to enmesh themselves in local communities.
It was the heart of the forest and there, in a marsh, lay a carpet of water lilies, their delicacy unveiled in the dawn light.
But the beauty belied the danger -- the Tofa Gala forest, on Mali's lawless border with Burkina Faso, was a haven for ruthless jihadists.
Guns in hand, French troops advanced on one side of the marsh, and their counterparts from Burkina Faso on the other.
Their goal: Assert control over an area where no troops had set foot for over a year.
Named Bourgou IV, the mission was the first official joint ground operation between the French army and the so-called G5 Sahel force, which pools troops from Burkina Faso, Chad, Mali, Mauritania and Niger.
In an exercise earlier this month, some 1,400 soldiers, 600 of them French, were deployed in the volatile region.
For jihadists, "it's an ideal area to hide and handle logistics," said Thibauld Lemerle, a French colonel.
Thousands of civilians and soldiers have died in violence across the Sahel which began when armed Islamists revolted in northern Mali in 2012.
The conflict has since swept into the centre of Mali and spilled into neighbouring Burkina Faso and Niger, inflaming ethnic tensions along the way.
Many thousands have fled their homes.
Belonging to a mosaic of groups from al-Qaeda to Islamic State and Ansarul Islam, the jihadists have exploited ethnic divisions and a feeling of abandonment to enmesh themselves in local communities.
France has some 4,500 troops in the region and the G5 Sahel force has a projected total of 5,000 -- a goal clouded by chronic funding, training and equipment problems.
They play a game of cat and mouse in this vast territory with a highly mobile enemy, able to vanish into the desert.
"They are here but hidden, we search for them but can't find them," said a non-commissioned officer, assault rifle in hand. "This is an impossible war."
A detonation occured -- a warning shot from one of the Burkinabe soldiers as a local passed by.
The troops walked on. They discovered two abandoned motorbikes suspected of belonging to jihadists and impounded them.
They marched for hours and found nothing.
"It's like looking for a needle in a haystack, he could be here, he could already be gone. Shooting can start without warning," said a lieutenant who gave his name as Julien.
The soldiers marched on. Ahead, six huts stood in the blazing sun and women and children clustered beneath an acacia tree. There were no men in sight.
The French troops searched the huts in silence. One cut open a mattress while another shakes mats.
"We're looking for means of communication and components used to make IEDs," said Pierrick, the head of the search party, referring to roadside bombs.
The troops found a few phones and set off on their two-hour hike to get back to their vehicles.
"We can't search like that, cutting up mattresses, see how those people were looking at us," one private from the search party said later, going over the events of the day.
"But it's the only way," another private said. "Imagine if a phone were hidden in the mattress".
A French officer explained the rationale behind the search missions. In areas under jihadist influence, he said, "everyone can be a potential enemy".
Caught between a rock and a hard place, locals pay a tough price.
Malian and Burkinabe forces have several times been accused of alleged human rights abuses. French forces are told to uphold strict rules of engagement.
The French army says there are mechanisms in place during joint operations to prevent incidents.
But a French official, who declined to be named, said that their partners do not always respect the rules.
The French and Sahel armies also differ widely in terms of equipment, which has its upsides and downsides.
One French officer said that French troops trundle slowly in armoured vehicles but the Sahel troops zip around on motorbikes.
A Burkinabe officer said the French security measures and loud convoys offer the jihadists time to escape. "It's normal that the French never find anything when they arrive," he saids. "With our motorbikes, we're more mobile."
But African troops are also far more exposed. Only days earlier, two Burkinabe soldiers riding a motorbike were killed by a roadside bomb.
In total some 170 Sahel soldiers have been killed since September in presumed jihadist attacks, including about 40 Malian soldiers who died in a single ambush in November.
One French soldier, by comparison, has died.
Despite years of training by French forces, the Sahel armies struggle with many problems.
Captain Wendimanegde Kabore, a Burkinabe unit commander, told AFP that securing food and water was especially difficult. On many evenings, Burkinable troops go to their French counterparts for a ration pack.
The arduous march is lightened at times.
French intelligence intercepted a message from one of the heads of Ansarul Islam just a few kilometres (miles) from the Bourgou operation's positions.
The army sent out 80 French soldiers in a bid to capture him, supported by drones and a Mirage 2000 warplane.
And towards the end of the same day, forces also caught wind of local informants who tip off the jihadists about army troops.
An armoured convoy took off in a cloud of dust, arriving at the village. Three men fled and threw objects into the undergrowth. One was arrested several minutes later.
Dressed in old jogging trousers and a sports vest, he stayed quiet.
"We took a telephone. He ran away when we arrived but the inhabitants stayed put, which is suspicious," said Julien, the lieutenant. "But we have nothing on him, so we're going to let him go."
About a hundred phones were confiscated over two weeks of Bourgou IV operations. Troops withdrew from the area on November 17.
Twenty-four people were killed or captured, according to the French army, and about 60 motorbikes seized.
Despite these seemingly meagre returns, military chiefs said they were pleased with the results, arguing that the operation had disrupted the jihadists and caused many to flee.
"Not every day is a rendezvous with glory," said Colonel Raphael Bernard. "But we work together, we shake things up and we fight".