The military leaders of Mali, Burkina Faso and Niger on Saturday signed a mutual defence pact, ministerial delegations from the three Sahel countries announced in Mali's capital Bamako.
The Liptako-Gourma Charter establishes the Alliance of Sahel States (AES), Mali's junta leader Assimi Goita posted on X, the social network formerly known as Twitter.
Its aim is to "establish an architecture of collective defence and mutual assistance for the benefit of our populations", he wrote.
The Liptako-Gourma region -- where the Mali, Burkina Faso and Niger borders meet -- has been ravaged by jihadism in recent years.
"This alliance will be a combination of military and economic efforts between the three countries", Mali's Defence Minister Abdoulaye Diop told journalists.
"Our priority is the fight against terrorism in the three countries."
A jihadist insurgency that erupted in northern Mali in 2012 spread to Niger and Burkina Faso in 2015.
All three countries have undergone coups since 2020, most recently Niger, where soldiers in July overthrew President Mohamed Bazoum.
The West African regional bloc ECOWAS has threatened to intervene militarily in Niger over the coup.
Mali and Burkina Faso quickly responded by saying that any such operation would be deemed a "declaration of war" against them.
- Mutual defence pact -
The charter signed on Saturday binds the signatories to assist one another -- including militarily -- in the event of an attack on any one of them.
"Any attack on the sovereignty and territorial integrity of one or more contracting parties shall be considered as an aggression against the other parties and shall give rise to a duty of assistance... including the use of armed force to restore and ensure security", it states.
It also binds the three countries to work to prevent or settle armed rebellions.
Mali has, in addition to fighting jihadists linked to Al Qaeda and the Islamic State group, seen a resumption of hostilities by predominantly Tuareg armed groups over the past week.
The escalation risks testing an already stretched army as well as the junta's claims that it has successfully turned around a dire security situation.
The successionist groups had in 2012 launched a rebellion before signing a peace agreement with the state in 2015. But that accord is now generally considered moribund.
The renewed military activity by those armed groups has coincided with a series of deadly attacks attributed mainly to the Al-Qaeda-linked jihadist alliance Support Group for Islam and Muslims (GSIM).
Mali's junta pushed out France's anti-jihadist force in 2022 and the UN peacekeeping mission MINUSMA in 2023.
French troops have also been pushed out of Burkina Faso, while Niger's coup leaders have renounced several military cooperation agreements with France.