Soldiers have gone on national TV in Niger to announce they have carried out a coup d'etat.
They said they had dissolved the constitution, suspended all institutions and closed the West African country's borders.
Niger's President Mohamed Bazoum has been held by troops from the presidential guard since early Wednesday.
In the TV announcement on Wednesday, Colonel Major Amadou Abdramane said the action follows the continuing deterioration of the security situation, and poor economic and social governance.
He has asked all external partners not to interfere with land and air borders that will remain closed until the situation has stabilised.
US Secretary of State Antony Blinken conveyed Washington's unwavering support in a call to Mr. Bazoum.
UN Secretary General Antonio Guterres also said he had spoken to the president and offered the UN's full support for him.
Mr. Bazoum is a key Western ally in the fight against Islamist militancy in West Africa.