Niger’s coup leaders have closed the country’s airspace until further notice, citing the threat of military intervention from their neighbours.
It comes after the Ecowas group of West African states demanded President Mohamed Bazoum be reinstated by Sunday.
Ecowas had warned that the junta could face military action and will now meet on Thursday to discuss next steps.
Meanwhile Mali and Burkina Faso, both also ruled by juntas, said they would send officials to Niger in solidarity.
Flightradar24 showed a transport plane had flown from Ouagadougou, the capital of Burkina Faso, and landed in Niger hours after airspace was closed.
The growing instability in the region compelled former colonial power France on Monday to warn its citizens against travelling to the Sahel region, and for those still there to be cautious due to anti-France sentiment.
“It is essential to limit travel, to stay away from any gatherings and to keep themselves regularly informed of the situation,” read a statement from the foreign ministry.
The junta in Niger on Sunday said it had information that “a foreign power” was preparing to attack the country, after military chiefs from Ecowas, a bloc of 15 countries including Nigeria, Senegal, Togo and Ghana, drew up a detailed plan for use of force.
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It had issued a 23:00 GMT Sunday deadline to Niger’s junta leaders to stand down and restore the elected president.
Earlier, Abdel-Fatau Musah, the bloc’s commissioner for political affairs, peace and security, said that while “all the elements” had been worked out about an “eventual intervention”, the body wanted “diplomacy to work”.
Bola Tinubu, president of the main regional power Nigeria, faced domestic political opposition to intervention, with senators voting against military action.
Local media reported that there was strong protests from senators from states near the long border between the two countries.
Mr Tinubu has repeatedly threatened Niger’s junta with force but needs approval from the National Assembly for any foreign venture.
Italy and Germany have both called for an extension to the deadline to reinstate President Bazoum so that a diplomatic solution can be found.
Mr Bazoum was deposed on 26 July, and Gen Abdourahmane Tchiani, commander of the presidential guard, later proclaimed himself the new leader.
The military takeover has been internationally condemned, France and the rest of the EU, as well as the UN and the US.
Hundreds of foreigners have been evacuated from Niger.
The coup leaders seem to be showing no sign of willingness to cede power, and on Sunday thousands of their supporters rallied defiantly at a stadium in the capital Niamey.
Burkina Faso and Mali earlier warned they would treat any outside military intervention in Niger as “a declaration of war” against them. The countries are both Ecowas members but have been suspended from the bloc since being taken over by the military.
Niger is a significant uranium producer – a fuel that is vital for nuclear power – and under Mr Bazoum was a key Western ally in the fight against Islamist militants in West Africa’s Sahel region.
Niger coup: The basics:
Where is Niger? It’s a vast country in West Africa, and one of the poorest countries in the world.
Why was there a coup? The military said it seized power because of insecurity and the economic situation, but there have been suggestions it came after reports the coup leader was about to be sacked.
What next? It’s feared the military may seek to switch allegiance to Russia and close French and US bases there; for their part, Niger’s neighbours have threatened to use force to end the coup.