Niger's Gen. Abdourahamane Tchiani — who took power after army officers toppled President Mohamed Bazoum on July 26 — said over the weekend that a transition of power would not go beyond three years.
He spoke after a delegation from the Economic Community of West African States visited Niger for a final diplomatic push before deciding whether to take military action against Niger's new rulers.
"The three-year transition is unacceptable," Abdel-Fatau Musah, ECOWAS commissioner for politics and security, told Al Jazeera channel in an interview broadcast on Monday.
"We want constitutional order to be restored as soon as possible."
In his televised address on Saturday, Tchiani charged ECOWAS with preparing to attack Niger by setting up an occupying force in collaboration with a foreign army, without referencing which country.
"If an attack were to be undertaken against us, it will not be the walk in the park some people seem to think," he said.
ECOWAS leaders say they have to act now that Niger has become the fourth West African nation since 2020 to suffer a coup, following Burkina Faso, Guinea and Mali.
The bloc has agreed to activate a "standby force" as a last resort to restore democracy in Niger and has said it ready to act though it is still pursuing diplomacy.
But it has given no date or details about any intervention.
The coup has heightened international worries over instability in the Sahel region, which faces growing jihadist insurgencies linked to Al-Qaeda and the Islamic State group.