Mali and Burkina Faso said Monday they had sent ECOWAS "formal notice" of their withdrawal from the West African bloc, with Niger expected to follow.
The foreign affairs ministry in Mali showed AFP a copy of the letter it sent to ECOWAS, while Burkina Faso's official news agency reported it had sent an official notice.
No information emerged from Niger, but the statements from its two neighbours stressed the common character of their move.
ECOWAS said earlier in a statement that it was awaiting "formal and direct notification" from the countries.
Under the bloc's statutes, withdrawal can't take effect for at least a year after official notification.
Mali, Burkina Faso and Niger were founding members of ECOWAS back in 1975, but the regional group has imposed sanctions on them following military coups that overthrew elected civilian governments.
On Sunday, the trio – who have formed an Alliance of Sahel States (AES) – jointly said ECOWAS had come "under the influence of foreign powers, betraying its founding principles" and was a "threat to member states and peoples".
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