A group of plainclothes police, soldiers and investigators huddle over the charred wreckage of a blue Mercedes near Senegal's dusty third city, Thies, the vehicle's two occupants blown apart by a bomb.

As jihadist bombers extend their reach across west Africa, hitting popular tourist venues in neighbouring nations in recent months, FBI and US military experts are coaching local counterparts on how to comb a crime scene for clues.

The victims of this car bomb are dummies and the crime scene a simulation, but the explosives are real -- part and parcel of the type of improvised explosives device (IED) attack the country has until now avoided.

"It's 9.30 am, the explosion went off in the trunk," a Senegalese army lieutenant reported back.

"The witness is a street hawker, Said Mohamed," he said after interrogating an FBI explosives specialist playing the role of a passerby.

"Two individuals, two terrorists, were trying to cross the border from Mauritania into Senegal, and the suicide vest they were carrying prematurely went off," said FBI supervisory special agent Victor Lloyd, explaining the scenario.

"Now the students are going to look around and gather whatever intelligence they can," added Lloyd, as the four-day simulation kicked off in the military base of Thies, some 70 kilometres east of the Senegalese capital, Dakar.

The session is part of a larger annual military exercise, known as Flintlock, that has been bringing together African, European and US counter-terrorism forces every year for the past decade.

But as the nature of the threat in west Africa changes, this is the first time police and even customs officials have been involved, said Billy Alfano, who works in a counter-terror unit within the US State Department.

A group of Senegalese police and soldiers secure the area, cordon it off with yellow tape and then rake it over for fragments of the bomb, tiny clues that could lead them to those behind the aborted "attack".

Part of the course is explicitly about "how to respond to a terrorist attack," Lloyd said, "which I hope never happens on Senegalese soil."

- 'No illusions' -

Those involved learn not only how to respond when an attack takes place but how to subsequently gather the right intelligence to prevent further bloodshed.

"Those individuals that you captured on the trail, they're not the ones that are actually orchestrating and planning the attacks," Lloyd pointed out.

Clad in a grey t-shirt, the FBI bomb expert -- who earlier played the role of a witness -- explained how vital the right questions could be in the aftermath of a bombing.

"We ask witnesses: what was the colour of the explosion, was it a thump in the chest?" he said.

"If they do a good job searching the bodies, they will find identity cards," he continued as the team puzzled over the smoking remains of the vehicle, whose roof was blown off in the blast.

It didn't take long for a Senegalese gendarme to announce they had several leads on where the components used in the explosives were bought.

He said he had also found "some addresses in the Thies region".

Unfortunately, the threat of a real-life attack is never far from the minds of those present who know that training can quickly turn into practical reality.

The tide of Islamist violence spreading in the restive Sahel region has been heightened by deadly attacks on Mali and Burkina Faso's capitals, with fears that jihadist groups are casting their net wider in search of targets in west Africa.

A few weeks after a mission in Kenya last year, one of the instructors said he had to return in April to help his former trainees, who were mobilised after the attack on Garissa university by Shebab Islamists that left 148 dead.

"We're not under any illusion that we're walking away after two weeks and turning the Senegalese into bomb experts," Lloyd said.

"I like to use the analogy that it's like car insurance," he said.

"You have it, (but) you hope you never have to use it."