Niger, Mali and Burkina Faso have announced they are leaving the Economic Community of West African States (Ecowas).
The junta-led countries had already been suspended from the bloc, which has been urging them to return to democratic rule.
The three governments said it was a “sovereign decision” to withdraw from Ecowas.
They were also founding members of the bloc, first established in 1975.
In a joint statement – that was read out on state broadcasters in the three countries – they said Ecowas had ” drifted from the ideals of its founding fathers and the spirit of Pan-Africanism.”
It goes on to say that Ecowas “under the influence of foreign powers, betraying its founding principles, has become a threat to member states and peoples,” adding that the bloc had failed to help them tackle the jihadist insurgencies in their countries.
Tensions between the bloc and the three countries have been tense after military coups took place in Niger in July, Burkina Faso in 2022 and Mali in 2020.
Ecowas has called on all three countries to return to civilian rule.
And in a response to Sunday’s announcement it said the three countries were “important members of the Community” and the bloc “remains committed to finding a negotiated solution to the political impasse”.
It also said it had not yet received formal notification from the countries about their withdrawal from the bloc.
According to the Ecowas treaty, member states wishing to withdraw must give written notice a year in advance, and continue to abide by its provisions during that year.
Despite suspension from the bloc, sanctions, negotiations and threats of military intervention, the military leaders have hardened their stance, accusing the bloc of being influenced by external powers.
In September, the three countries formed a mutual defence pact called The Alliance of Sahel States, distanced themselves from former colonial power France and strengthened ties to Russia.
The three military leaders have argued that they want to restore security before organising elections as they struggle to contain insurgencies linked to al Qaeda and Islamic State.
Niger’s military leaders have said they want up to three years for a transition back to civilian rule.
The military government in Mali had pledged to hold elections in February, but that has now been pushed back to an unknown date.
Meanwhile, Burkina Faso has set elections for this summer, but authorities there say the fight against the insurgents remains the top priority.
A delegation from Ecowas was due to travel to Niamey for a meeting with the junta in Niger on Thursday to discuss sanctions on the country.
However, the aircraft that was meant to take the delegation there developed “technical problems” in Abuja and the meeting was postponed.