West African nations have approved armed intervention in Niger “as soon as possible”, the Ivory Coast president says, following a meeting to discuss the coup.
At the meeting, leaders of the Ecowas regional bloc said they had agreed to deploy a “standby” military force.
However, they have not given any details of the size of the force.
Nigeria’s President Bola Tinubu said the use of force would be a “last resort”.
A military junta seized power in Niger on July 26.
After the Ecowas meeting, Ivory Coast’s Alassane Ouattara said Ecowas had intervened in African countries in order to restore constitutional order before.
“Today we have a similar situation in Niger, and I like to say that Ecowas cannot accept this,” he said.
Mr Ouattara said the Ivory Coast would provide a battalion of 850 to 1,100 men, and said soldiers from Nigeria and Benin would also be deployed.
Omar Touray, president of the Ecowas group, said members had decided “to order the deployment of the Ecowas standby force to restore constitutional order in Niger”.
He did not set out further details of what the force it intends to assemble might look like or what action it might take.
Abdel Musah, the bloc’s security commissioner, told the BBC that Ecowas would not allow the junta to stay in power during a transitional period like their counterparts in Burkina Faso and Mali.
However, he said the junta was not willing to have direct contact with Ecowas, making negotiations difficult.
The US and UN say they are concerned about the health and safety of deposed president Mohamed Bazoum, who has spent more than two weeks under house arrest.
Ahead of Thursday’s meeting, Muslim clerics from northern Nigeria, which shares a long border with Niger, had urged Nigerian President Tinubu against using force to oust the coup leaders.
But speaking after the meeting, he said: “No option is taken off the table, including the use of force as a last resort.
“If we don’t do it, no one else will do it for us.”
The coup leaders have warned they will defend themselves against any intervention.
Ecowas had issued a deadline of last Sunday to the Niger junta to restore the democratically-elected government, but it was ignored.
Instead, military leaders named a new ruling cabinet.
Both the US and France have military bases in Niger, which have been used as part of efforts to tackle jihadist groups in the wider Sahel region.
US Secretary of State Antony Blinken told the BBC earlier this week that he believes Russia’s Wagner mercenary group is “taking advantage” of the instability in Niger.