When the soldiers reached the end of the road, they descended from their trucks and motorbikes and partially deflated the tyres to make it easier going across the soft terrain of eastern Mali.

Then they rumbled onwards in the moonlight along a grassy trail that snaked through Islamic State's stronghold there.

"We are in an area where there have been numerous thefts of cattle recently. Remain vigilant," said a senior officer as a herd of cows slowed the convoy's progress. "We are entering a region of armed terrorist groups."

The troops were part of the Takuba Task Force, a group of elite soldiers from across Europe charged with turning the tide in a decade-long Islamist insurgency that has killed thousands of civilians in the Sahel, the band of arid terrain south of the Sahara Desert.

The force is also at the centre of a political row. Takuba was established as a partial successor to Barkhane, France's 5,000-strong counter-terrorism operation in the Sahel that French President Emmanuel Macron wants to reduce by as much as half. French troops are still involved in the new mission.

Mali, however, says France is abandoning its former colony and its ruling junta is seeking a deal with Russian military contractor the Wagner Group, a move France is trying hard to block. read more

WATCHING US

The methods were new, however. Takuba is using smaller, more mobile units with lighter equipment that travel mostly at night and that commanders say better suit the conflict.

Game-changing tactics are sorely needed in the Sahel, where violent attacks across Mali, Niger and Burkina Faso increased eight-fold in 2015 to 2020, according to the United Nations. This has driven 2 million from their homes and left swathes of territory out of governments' control.

On the ground in Mali, the going was tough even with motorbikes and non-armoured vehicles, said a Reuters reporter who was on the Takuba mission.

The area near the Niger River is familiar to the militants, but to the French and Estonian troops it was a constantly shifting landscape of rocky outcrops, sand, grassland and swamps.

On the second day, not far from a village where the soldiers said militants were hiding out, heavy rain flooded their makeshift camp. The trucks' tyres were engulfed in mud and it took three hours to get them out. The blare of their revving engines pierced the morning calm, and exposed their position.

"Terrorists have a very developed network of informants, which we call 'doorbells', able to provide information on our actions," said the senior officer, who asked not be named.

"As soon as they become aware of or suspect a force in the area, they either seek to hide their weapons and blend in with the population, or to flee."

By the time they got to the village, there was no sign of militants. They arrested two men in possession of walkie-talkies and huddled around to decipher the voices crackling through the receiver.

"The terrorists are watching us right now," the officer said.

Reporting by Paul Lorgerie; Editing by Edward McAllister and Angus MacSwan