The 15-member Economic Community of West African States (ECOWAS), and the eight-member West African Economic and Monetary Union, could suspend Niger from its institutions, cut off the country from the regional central bank and financial market, and close borders.
Niger's eastern neighbour Chad, a non-member of both regional organisations, has been invited to the ECOWAS summit on Sunday, a statement from the Chadian president's office said on Saturday.
Niger is one of the poorest countries in the world, receiving close to $US2 billion ($A3 billion) a year in official development assistance, according to the World Bank.
It is also a security partner of former colonial power France and the US, which both using it as a base to fight an Islamist insurgency in West and Central Africa's wider Sahel region.
The West African leaders could also for the first time consider a military intervention to restore President Mohamed Bazoum who was ousted when General Abdourahamane Tiani was declared the new head of state on Friday.
Ahead of the summit, the military leaders in Niger warned against any military intervention, in a statement read on national television on Saturday night.
"The objective of the (ECOWAS) meeting is to approve a plan of aggression against Niger through an imminent military intervention in Niamey in collaboration with other African countries that are non-members of ECOWAS, and certain western countries," junta spokesman Colonel Amadou Abdramane said.
"We want to once more remind ECOWAS or any other adventurer, of our firm determination to defend our homeland."
The junta issued a second statement on Saturday night inviting citizens in the capital to take to the streets from 7am local time to protest against ECOWAS and show support for the new military leaders.
The military coup in Niger has been widely condemned by its neighbours and international partners who have refused to recognise the new leaders and have demanded that Bazoum be restored to power.
Bazoum has not been heard from since early Thursday when he was confined within the presidential palace, although the EU, France and others say they still recognise him as the legitimate president.
The EU and France have cut off financial support to Niger and the US has threatened to do the same.
After an emergency meeting on Friday, the African Union issued a statement demanding the military return to their barracks and restore constitutional order within 15 days. It did not say what would happen after that.
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