The imminent deployment of 300 US soldiers in Cameroon is intended to provide nations around Lake Chad with what they most lack in the battle against Boko Haram: reliable intelligence.

On Thursday and Friday, suicide bombers from the Islamist sect slew dozens of people in attacks on Maiduguri in northeast Nigeria, where the radical movement first emerged. The insurgency has claimed at least 17,000 lives since 2009.

Cameroon, Chad and Niger, which all have borders with Nigeria in the Lake Chad region, have formed a military alliance with Nigeria and Benin to battle the extremists, who this year declared allegiance to the Islamic State.

Nigeria's neighbours have each been hit by bombers, often women or adolescent girls, who detonate their devices in crowded places such as open markets. Bans on concealing clothes, searches and close scrutiny have prevented some attacks, but others come without warning.

National intelligence services are historically best known for monitoring the activities of the domestic opposition, rather than tackling threats from the likes of Boko Haram, whose violence has uprooted about 2.5 million people.

Heads of state in the Lake Chad region have several times pleaded for international assistance to the multinational task force created this year to take the war to the enemy.

France already provides some forms of intelligence. Paris has deployed a strong military presence on the ground, including Operation Barkhane, with its headquarters in the Chadian capital N'Djamena, set up to fight jihadists in the Sahel.

- 'Stay until no longer needed' -

Last year, Washington provided Nigeria with intelligence, surveillance and reconnaissance expertise in the hunt for more than 200 schoolgirls abducted by Boko Haram from their school.

Analysts have seen alleged military abuses such as arbitrary detention of Boko Haram suspects in both Nigeria and Cameroon as having hit their ability to gather on-the-ground intelligence from civilians.

The US meanwhile has reservations about selling arms to Nigeria over concerns of rights violations by its military.

The US military 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 will now also be monitoring Boko Haram.

The first 90 men out of 300 US soldiers arrived on Monday in Cameroon, where they will be stationed at the northern town of Garoua, which is already a base for the Cameroonian air force to fly sorties to bomb Boko Haram infiltrators.

"It will be part of a broader regional effort to stop the spread of Boko Haram and other violent extremist organisations in West Africa," White House spokesman Josh Earnest said Wednesday.

The US forces will carry out surveillance and airborne reconnaissance activities, with intelligence duties, but will not take part in combat, Earnest added.

When President Barack Obama announced the move to Congress on Wednesday, his aide stressed that the deployment did not arise from a big change of strategy on Washington's part.

But in Cameroon, a senior army officer who asked not to be named said that the arrival of US troops "marks a development" on the ground.

Until now, US assistance was limited to training, notably in tackling mines and defusing explosives carried by would-be suicide bombers, the officer said. The United States has military training agreements with several African countries.

"This announcement in fact marks a development in the type of support given to Cameroon by the Americans," the officer said, particularly since there is no time limit on the mission.

The troops will stay "until their support is no longer needed", Obama said in his letter to the leaders of both houses of Congress.

Nigerian President Muhammadu Buhari, who made the struggle against Boko Haram a priority as soon as he took up office in May, has given the armed forces until the end of the year to crush the Islamist movement.

On Wednesday, Buhari said the military was "well-positioned to meet the December deadline which they have been given".

Campaigns by the armies of the region since the beginning of 2015 have taken back most of the territory held by the insurgents.

But Boko Haram maintains strongholds in areas that are difficult to access, such as the Sambisa forest, the Mandara mountains and the numerous islands of Lake Chad, where it will call for lengthy military operations to rout the Islamists.