Leaders of Burkina Faso, Chad, Mali, Mauritania and Niger gathered for a one-day meeting aimed at beefing up coordination in the battle against jihadists who have killed hundreds of civilians and inflicted crippling economic damage.
On the eve of the summit, 14 civilians were killed by insurgents in a pre-dawn attack at Kain in northern Burkina Faso near the Mali border, the military said.
It said it carried out retaliatory air strikes and land operations in three northern provinces, "neutralising" 146 fighters, a claim that could not be independently confirmed.
"Burkina Faso, the host of this summit, which used to be among the most peaceful countries in the world... is today the victim of attacks by terrorists with regressive aims," said former Burundian president Pierre Buyoya, the African Union's representative at the summit.
"The African Union expresses its solidarity and compassion for the Burkinabe government and people and urges them to mobilise to stand together against the destabilising actions of the terrorist groups. It encourages them to close off any gaps in which the enemy can flourish."
Tight security was in place on Tuesday. A key highway linking the airport and the conference venue was closed off to non-summit traffic, and armed troops were deployed at regular intervals.
The Islamist revolt in the Sahel took off after chaos engulfed Libya in 2011. Jihadist attacks erupted in northern Mali as Boko Haram arose in northern Nigeria.
As the toll spiked, a French-backed scheme was launched in 2015 with the goal of deploying a 5,000-man joint force among five nations in the front line.
But lack of funding and training, as well as poor equipment, have greatly undermined the initiative, and last June the force's headquarters in Mali were hit in a devastating suicide attack claimed by an al-Qaeda-linked group.
The G5's problems have given rise to long periods of apparent inactivity, although on Sunday, its commander General Hanena Ould Sidi, a Mauritanian, said the force had carried out three operations since January 15. He gave no further details.
The attacks in Burkina Faso began in the country's north in 2015 but then spread to the east. Nearly 300 people have been killed, according to an AFP toll.
The capital Ouagadougou has been hit three times, most recently in March 2018, and almost 60 people have died here.
Last month, President Roch Marc Christian Kabore carried out a major reshuffle of the country's security apparatus, sacking the chief of the armed forces and replaces the ministers for defence and security.