The Economic Community of West African States, which has sent military forces into troubled member states in the past, had told the junta to stand down by Sunday, but coup leaders instead closed Niger's airspace and pledged to defend the country.
ECOWAS spokesperson Emos Lungu said the bloc would hold an extraordinary summit to discuss Niger on Thursday in Abuja, the Nigerian capital, where it has its headquarters.
State television announced the move to close the country's airspace Sunday night, hours before the deadline set by ECOWAS. The mutinous soldiers accused foreign powers of preparing an attack and threatened “an energetic and immediate response” to any attempt to fly over the country.
A spokesman for the coup leaders, Col. Maj. Amadou Abdramane, noted “the threat of intervention being prepared in a neighboring country,” and said Niger's airspace will be closed until further notice. The junta also asserted that two central African countries are preparing for an invasion, but did not say which ones, and called on the country's population to defend it.
International airlines have begun to divert flights around the airspace of Niger, which the United States and others had seen as the last major counterterrorism partner in the vast Sahel region, south of the Sahara Desert, where groups linked to al-Qaida and the Islamic State group are expanding their influence. The future 1,100 U.S. military personnel in Niger is not immediately known.
In Mali, the armed forces said Monday that it and Burkina Faso, both neighbors of Niger run by military juntas, were sending a delegation of officials to Niger to show support. Both countries have said they would consider any intervention in Niger as a “declaration of war” against them.
Regional tensions have mounted since Niger's coup nearly two weeks ago, with the mutinous soldiers detaining Bazoum and installing Gen. Abdourahmane Tchiani, former head of the presidential guard, as head of state. Analysts say the coup is believed to have been triggered by a power struggle between Tchiani and the president, who was about to fire him.
It was not immediately clear what ECOWAS will do now that Sunday's deadline has passed. There was no sign of military forces gathering at Niger's border with Nigeria, the likely entry point by land.
On Saturday, Nigeria’s Senate pushed back on the plan to invade, urging Nigeria’s president, the bloc’s current chair, to explore options other than the use of force. ECOWAS can still move ahead, as final decisions are made by consensus by member states.
A former British army officer who worked in Nigeria said military officials there told him Monday that President Bolu Tinubu had not given orders to use military force. He spoke on condition of anonymity because of the sensitivity of the situation.
Guinea and neighboring Algeria, which is not an ECOWAS member, have come out against against the use of force. Senegal’s government has said it would participate in a military operation if it went ahead, and Ivory Coast has expressed support for ECOWAS’ efforts to restore constitutional order.
The junta does not appear interested in negotiation. An ECOWAS delegation sent to Niger last week for hours of talks was not allowed to leave the airport and met only with Tchiani's representatives.
At a rally on Sunday, thousands cheered junta leaders who said their loyalty will not be betrayed.
The junta is using anti-French sentiment among the population to shore up its support base and has severed security ties with France, which still has 1,500 military personnel in Niger for counterterrorism efforts. On Monday, France’s ministry of foreign affairs formally discouraged any travel to Niger, Burkina Faso or Mali, and called on French nationals to be extremely vigilant.
Niger's junta also has asked for help from the Russian mercenary group Wagner, which operates in a handful of African countries including Mali.
Many people, largely youth, have rallied around the junta, taking to the streets at night to patrol after being urged to guard against foreign intervention.
"While they (jihadists) kill our brothers and sisters ... ECOWAS didn’t intervene. Is it now that they will intervene?” said Amadou Boukari, a coup supporter at Sunday's rally. “Shame on ECOWAS."
But others have expressed concern about the junta's tightening grip.
One official, who spoke on condition of anonymity to The Associated Press because they were not authorized to comment, said the junta is scaring people into joining it.
African and Western allies have imposed sanctions and cut aid to Niger in attempts to pressure the junta to step down.
Information for this report The Associate Press and Reuters.