Niger closed its airspace on Sunday until further notice, citing the threat of military intervention from the West African regional bloc after coup leaders rejected a deadline to reinstate the country's ousted president.
Earlier, thousands of junta supporters flocked to a stadium in Niamey, the capital, cheering the decision not to cave in to external pressure to stand down by Sunday following the July 26 power grab.
The coup, the seventh in West and Central Africa in three years, has rocked the Sahel region, one of the poorest in the world. Given its uranium and oil riches and its pivotal role in a war with Islamist militants, Niger holds importance for the U.S., Europe, China and Russia.
Defense chiefs of the Economic Community of West African States (ECOWAS) have agreed a possible military action plan, including when and where to strike, if the detained president, Mohamed Bazoum, is not released and reinstated by the deadline.
"In the face of the threat of intervention that is becoming more apparent ... Nigerian airspace is closed effective from today," a junta representative said in a statement on national television on Sunday evening.
He said there had been a predeployment of forces in two Central African countries in preparation for an intervention but did not give details.
ECOWAS did not respond to a request for comment on what its next steps would be, or when exactly on Sunday its deadline expires. A spokesman earlier said it would issue a statement at the end of the day.
Blasting military tunes and tooting vuvuzela horns, over 100 junta supporters this weekend set up a picket near an air base in Niamey -- part of a citizen movement to offer nonviolent resistance in support of the junta if needed.
As organizers led chants of "Vive Niger," much of the emotion appeared directed against ECOWAS as well as former colonial power France, which said on Saturday it would support regional efforts to overturn the coup, without specifying if that included military assistance.
"The Nigerien people have understood that these imperialists want to bring about our demise. And God willing, they will be the ones to suffer for it," said pensioner Amadou Adamou.
Niger last week revoked military cooperation agreements with France, which has between 1,000 and 1,500 troops in the country.
Sunday's television broadcasts included a roundtable debate on encouraging solidarity in the face of ECOWAS sanctions, which have led to power cuts and soaring food prices.
The bloc's military threat has triggered fears of further conflict in a region already battling the deadly Islamist insurgency that has killed thousands and forced millions to flee.
Any military intervention could be complicated by a promise from juntas in neighboring Mali and Burkina Faso to come to Niger's defense if needed.
Bazoum's prime minister, Ouhoumoudou Mahamadou, said on Saturday in Paris that the ousted regime still believed a last-minute agreement was possible.
On Sunday, Italy said it had reduced its troop numbers in Niger to make room in its military base for Italian civilians who may need protection if security deteriorates.