Niger's President Mohamed Bazoum is in good health after being taken captive by his own presidential guard, the French foreign minister has said.
Catherine Colonna told AFP news agency the coup was not "final".
She said Mr Bazoum had spoken to Emmanuel Macron and added there was a "way out" for the coup plotters if they listened to the global community.
On Thursday, coup supporters attacked the headquarters of the ousted president's party.
They set it on fire, stoning and burning cars outside. The small group of arsonists had broken away from a larger show of support for the coup leaders outside parliament, where Russian flags were on show.
The army has now given its backing to the troops who detained Mr Bazoum on Wednesday. Russia has joined other countries and the UN in calling for his release.
The 64-year-old was elected as Niger's president two years ago, and has been a key Western ally in the fight against Islamist militants in West Africa.
The US and France, the former colonial power, both have military bases in the uranium-rich country - and have strongly condemned the coup.
US Secretary of State Antony Blinken called up Mr Bazoum promising Washington's "unwavering support".
The United Nations (UN) said it has suspended its humanitarian operations in Niger. It is unclear whether the coup was the reason behind the suspension.
The UN has previously said more than four million people in Niger are in need of humanitarian assistance.
On Thursday, UN Secretary-General Antonio Guterres demanded the release of Mr Bazoum "immediately and unconditionally".
Mr Bazoum tweeted a defiant statement on Thursday morning: "The hard-won achievements will be safeguarded. All Nigeriens who love democracy and freedom will see to it."
His foreign minister has also been trying to rally support and urge dialogue, but the army chief of staff said he was backing the takeover to avoid fighting within the armed forces.
It remains unclear who is really in charge of Niger as the junta has not announced its leader.
State TV has been repeating the late-night coup announcement interspersed with patriotic music and Quranic verses - and its usual lunchtime news bulletin was not aired.
But in the capital, Niamey, shops and markets opened for business and after delays due to heavy rain early in the morning, coup supporters took to the streets.
The hundreds who gathered outside the National Assembly had some Russian flags, while others held up hand-written signs saying: "Down with France" and "Foreign bases out".
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Police later fired tear gas to disperse those who had gone to the headquarters of the ruling party, where party activists ran away when they saw the protesters coming.
Some people were injured in the fracas and the burnt-out carcasses of vehicles now surround the PNDS Tarraya party building.
The coup supporters accuse the party of corruption and not doing enough to improve the security situation and end the long-running jihadist insurgency.
Two neighbouring countries, Mali and Burkina Faso, have experienced coups triggered by Islamist uprisings in recent years.
In both countries the new military leaders have moved closer to Russia after falling out with France.
"I hope they will install good security in the city and help us to achieve better conditions, because we have good resources. I don't care if they just want to follow Burkina Faso or Mali," Djibo, a supporter of the coup, told the BBC.
A number of well-known pro-Kremlin commentators on Telegram - one of the few major social media platforms not banned in Russia - have been posting comments in support of the coup, saying it is an opportunity for Russia and Wagner to get into Niger.
For the moment, there is no evidence of any Russian involvement in this takeover. Russian Foreign Minister Sergei Lavrov said constitutional order in Niger should be restored, Reuters says, quoting Russia's state-owned Tass news agency.
Some civil society groups in Niger have been calling for a move away from France and towards Russia in recent weeks.
The junta has reprimanded France for violating the closure of the country's borders after a military plane landed at an air-force base on Thursday morning.
The takeover was announced by a spokesman, Col Maj Amadou Abdramane, who said the takeover was instigated by the deteriorating security situation "and poor economic and social governance".
But Niger's private L'Enqueteur newspaper has suggested the coup was prompted by President Bazoum's attempt to remove Gen Abdourahamane Tchiani as commander of the presidential guard.
The turn of events has split people in Niger - and some are shocked and upset.
While it was underway on Wednesday, hundreds of the president's supporters defied the soldiers to protest and call for the military to return to the barracks.
They dispersed after warning shots were fired - the only gunfire heard in this bloodless seizure of power.
"The coup is very regrettable. It makes me sad because I want the best for our country. Niger will regress now," Mustapha, a resident of Niamey sheltering at home with his wife and three-year-old son, told the BBC.
Niger's Foreign Minister Hassoumi Massoudou has called on the population to oppose the takeover.
In an interview with the channel France24, he said that the situation could still be resolved through dialogue and said envoys sent from neighbouring Nigeria were talking to the military.
Benin's President Patrice Talon who planned to a mediation mission on behalf of the West African regional bloc, Ecowas, has had to abandon his trip because of the border closure.
The vast arid country on the edge of the Sahara desert - one of the world's poorest nations - has experienced four coups since independence from France in 1960, as well as numerous attempted coups.
BBC
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