Mali says it will send a joint delegation with Burkina Faso to Niger to express their solidarity.
The announcement comes a day after the generals – who seized power in Niger – defied an ultimatum to reinstate the elected president or face the possibility of armed intervention from other West African states.
The military junta said it had closed Niger’s airspace and was preparing to defend its territory.
Despite the ultimatum, members of regional grouping Ecowas are divided on whether to take military action.
Nigeria and Ivory Coast are among those insisting that President Mohamed Bazoum must be reinstated.
But the military governments in Mali and Burkina Faso have said they would side with the coup leaders if they were attacked