A statement released by the Chadian and Mauritanian officials said the two nation's "take note and respect the sovereign decision" made by Burkina Faso and Niger to leave the alliance, following the footsteps of Mali who announced withdrawal in 2022.
The G5 Sahel, which included Mauritania, Burkina Faso, Chad, Mali and Niger, was created in 2014, with an anti-jihadist force added in 2017, backed by France.
Chad and Mauritania said they "will implement all necessary measures in accordance with the G5 founding convention, notably Article 20," which says the alliance can be dissolved at the request of at least three member states.
In announcing their withdrawal on Saturday, Burkinabe and Nigerien military officials did not explicitly call for its dissolution. However, the fate of the grouping had seemed sealed even before Mali's junta announced it was quitting in 2022.
The joint military force has achieved meagre results — on the ground, few joint G5 operations have actually been carried out and the region’s security situation has continued to deteriorate.
Violence has spread across West Africa and thousands of civilians and fighters have been killed while millions of people displaced from their homes.
The violence has also contributed to political instability in the region, which has seen a succession of military coups — Mali in 2020, Burkina Faso in 2022 and earlier this year in Niger.
Stressing their sovereignty, Mali, Burkina Faso and Niger have increasingly turned their backs on former colonial power, France, and its European partners.
Their military rulers in the three nations have accused Paris of having an outsize role after years of French deployments on their territories.
This year, the West African nations — who are all battling long-running jihadist insurgencies — have come together to support the creation of an Alliance of Sahel States, establishing closer economic ties and mutual defense assistance.
Mali, Burkina Faso and Niger's foreign ministers last week recommended creating a confederation as part of a long-term goal of uniting the West African neighbors within a federation.
Burkina Faso and Niger said in their statement on Saturday that they had decided "to quit all instances of the G5 Sahel, including the joint force."
The decision took effect on November 29, they added.
"The organization is failing to achieve its objectives," Burkina Faso and Niger said.
"Worse, the legitimate ambitions of our countries, of making the G5 Sahel a zone of security and development, are hindered by institutional red tape from a previous era," the two nation's added.
"The G5 Sahel cannot serve foreign interests to the detriments of our people, and even less the dictates of any power in the name of a partnership that treats them like children, denying the sovereignty of our peoples," the statement by the two nations read.
Mali accused the G5 Sahel of being a tool of an "outside" state.