On national television, soldiers in the Republic of Niger in West Africa announced a coup.
They claimed to have locked the country's borders, repealed the constitution, and suspended all institutions. Since early Wednesday, soldiers from the presidential guard have kept Niger President Mohamed Bazoum in custody.
In a phone call, US Secretary of State Antony Blinken assured him of Washington's "unwavering support."
Also claiming to have spoken with the president, UN Secretary-General Antonio Guterres extended the UN's complete support.
Mr Bazoum is a crucial ally of the West in the conflict with Islamist militancy in West Africa.
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In recent years, two neighbouring countries, Mali and Burkina Faso, have experienced coups triggered by jihadist uprisings.
The new military commanders in both nations are at odds with France, the old colonial power that had dominated Niger as well.
Unknown to the public, Mr Bazoum remarked in a tweet on Thursday morning that the "hard-won gains will be safeguarded" and that Nigerians who value democracy will take care of the situation.
Hassoumi Massoudou, the foreign minister, proclaimed himself to be the head of state and urged all Democrats to "make this adventure fail."
Col. Maj. Amadou Abdramane made the following statement on television on Wednesday: "We, the defence and security forces... have decided to put an end to the dictatorship, you know.
This comes after weak economic and social governance and the worsening security situation.
The heads of the ministries would handle day-to-day operations, he added, adding that all of the nation's institutions had been halted.
He said, "All external partners are requested not to interfere." "Until the situation has stabilized, land and air borders are closed."
He stated that until further notice, a nighttime curfew would be in place from 22:00 to 5:00 local time.
The National Council for the Safeguard of the Homeland (CNSP), according to Col Maj Abdramane, was represented by the soldiers.
Mr Blinken demanded the release of President Bazoum following the soldiers' television broadcast.
"What it clearly constitutes," he said at a news conference in New Zealand, "is an attempt to seize power by force and to disrupt the constitution."
