The African Union and the European Union called on Niger's military junta to end their regime.
The AU demanded Niger's military "return to their barracks and restore constitutional authority" within 15 days. The EU intensified pressure on the coup leaders Saturday by suspending security cooperation with the terrorist-hit country.
General Abdourahamane Tiani, head of the Presidential Guard since 2011, appeared on state television on Friday to declare himself the troubled West African country's new leader.
His forces have confined democratically elected President Mohamed Bazoum to his official residence in the capital Niamey since Wednesday, in a putsch Tiani presented as a response to "the degradation of the security situation" linked to terrorist bloodshed.
The AU and the EU joined the chorus of international condemnation of the power grab, the latest to strike the Sahel region.
Niger's neighbors Mali and Burkina Faso have both undergone two military coups since 2020, fuelled by anger at a failure to quash long-running insurgencies by terrorists linked to the Daesh terrorist group and al-Qaida.
The AU's Peace and Security Council "demands the military personnel to immediately and unconditionally return to their barracks and restore constitutional authority, within a maximum period of fifteen (15) days," it said in a communique following a meeting Friday on the coup.
It "condemns in the strongest terms possible" the overthrow of the elected government and expressed deep concern over the "alarming resurgence" of military coups in Africa.
The EU's diplomatic chief Josep Borrell on Saturday said the bloc would not recognize the putschists and announced the suspension of security cooperation with Niger.
"The European Union does not recognize and will not recognize the authorities from the putsch in Niger," Borrell said in a statement.
"All cooperation in the security field is suspended indefinitely with immediate effect," in addition to the end of budgetary aid, he added.
Bazoum "remains the only legitimate president of Niger," the statement said, calling for his immediate release and holding the coup leaders to account for the safety of the president and his family.
Borrell said the EU was ready to support future decisions West Africa's regional bloc took, "including the adoption of sanctions."
Leaders from the Economic Community of West African States will meet on Sunday in Abuja to discuss the coup, Nigerian President Bola Tinubu said.
French President Emmanuel Macron was due to chair a meeting of his Defense and National Security Council on the coup on Saturday afternoon, the presidency said.
France, Niger's former colonial power, has 1,500 soldiers in the country. The United States has around 1,000 troops on the ground.
Tiani, 59, has shunned the limelight despite a stellar military career which has seen him lead the 700-member presidential guard since 2011.
He is a staunch ally of former president Mahamadou Issoufou, Bazoum's predecessor, who appointed him head of the presidential guard.
Sources close to Bazoum told AFP that he had been considering replacing Tiani as the head of the elite unit.
Tiani meanwhile began shunning "official ceremonies and activities" of the president and sent his deputy Colonel Ibroh Amadou Bacharou, also a member of the new junta, to represent him, one source close to Bazoum said.
Landlocked Niger is one of the world's poorest nations, often ranking last in the U.N.'s Human Development Index, despite vast deposits of uranium.
It has had a turbulent political history since gaining independence in 1960, with four coups as well as numerous other attempts — including two previously against Bazoum.
The 63-year-old has been one of a dwindling group of elected presidents and pro-Western leaders in the Sahel as juntas in Mali and Burkina Faso turn away from traditional allies and toward Russia.
