West Africa's armed forces, police and governments need to ramp up cross-border links to contain Islamist groups now increasingly staging spectacular attacks on civilian targets, US and local top brass said this week.

The region faces "an adversary that does not recognise geographic boundaries," General David Rodriguez, head of the US Africa command, said at the closing ceremony this week of the continent's US-led Flintlock military exercise.

The three-week manoeuvres bring together African, European and US counter-terrorism forces every year, but 2016's edition of 28 nations took on an edge of urgency.

"I am certain that we will all have the opportunity to execute what we have learned together here," Rodriguez told dignitaries gathered in the northern Senegalese city of Saint-Louis.

Security at the closing ceremony was remarkably light, underlining the fact that stable countries such as Senegal have only very recently faced the reality of an Islamist threat.

Children ambled up to the military parade and took seats while a troupe of dancers later entertained over chicken and cola.

But attacks in recent months on luxury hotels in the capitals of neighbouring Mali and Burkina Faso left dozens dead, giving Flintlock participants a very clear heads-up, said exercise director Lt. Colonel William Rose.

Mali was "always a topic of discussion, as well as Burkina Faso," he said. "That came up all the time."

Rose pointed to several lessons from those two attacks, including the importance for police of comprehensively gathering evidence to track down perpetrators and their backers once the violence is over.

"What was really different was a large incorporation of law enforcement," Rose said as police and customs officials were integrated into Flintlock's counter-terror work for the first time.

West African countries must encourage their militaries to work "with other government agencies as well as other civilian government entities," he added.

To lead by example, the US military brought over FBI explosives experts and State Department officials to aid in the simulation of a botched suicide bombing in the course of the exercise.

"The bad guys share intelligence, they talk to each other," FBI Supervisory Special Agent Victor Lloyd told AFP during the training.

The biggest ever deployment of Senegal's resources into this year's Flintlock was aimed at "reinforcing our capacities of prevention, action and reaction in the face of diffuse and cross-border threats," said Mamadou Sow, Chief of Staff of Senegal's armed forces, which co-hosted the event with Mauritania.

Police were far more likely than soldiers to come into contact with civilians day-to-day, so the training centred on "raising consciousness on security issues that have a direct impact on civilians' daily lives," he added.

- Nebulous groups -

Nebulous entities such as Al-Qaeda in the Maghreb, with roots farther north in Algeria but fighters roaming Mali, Niger and Mauritania, cause particular concern.

Mali in particular is afflicted by a security problem so persistent that UN, French and domestic forces are all attempting to keep order after the brief occupation of northern cities by Al-Qaeda-linked groups in 2012.

During the course of Flintlock's operations, the French prime minister and defence chief visited troops in Mali and paid respects to victims of a recent hotel attack in Burkina Faso, with diplomats describing an enemy radically changed in the last three years.

"(The Islamists) wanted to occupy territory and form strongholds... so it's a show of weakness even if it's more spectacular, when a suicide bomber shows up at a hotel to blow himself up," said one French official, requesting anonymity due to his position.

"Those methods didn't exist before," the official added.

Some of the Flintlock group, including Nigeria, Chad and Niger, are already fighting entrenched battles against other sprawling Islamist groups such as Boko Haram.

Meanwhile US advisers and special operations troops are playing a growing role in the global fight against Islamist extremists, including in Iraq, Syria and Libya.

The Pentagon is considering sending military advisers to Nigeria to train local troops to fight Boko Haram insurgents, a US official said Friday.

It is also active in Niger, where it uses drones to watch over the broad strip of Sahel territory on the southern side of the Sahara. The pilotless aircraft also monitor Boko Haram activities.