A group of protesters gathered near the Niger embassy in Paris on Saturday to show their support for democracy and President Mohamed Bazoum.
Demonstrators held signs and Niger flags while calling for the release of Bazoum, who was ousted in a coup last week by rebelling soldiers.
Niger Prime Minister Ouhoumoudou Mahamadou joined the demonstration said he was worried about the evolution of the situation but acknowledged there was still time left on the ultimatum and that a successful negotiation could still be possible.
“We are indeed concerned to see how the situation is developing," said Mahamadou.
"We hope that through dialogue we can resolve this issue. There's still time to comply with the ultimatum. The deadline is tomorrow.
"We still hope that negotiations will prevail and that there will not necessarily be military intervention. We are still hoping that the coup leaders who are holding our comrade, President Mohamed Bazoum, will release him."
Mahamadou was in France because he was unable to return to Niger when the borders shut, which happened as he was travelling to Italy for international meetings.
The regional bloc ECOWAS presented Niger's junta with a Sunday deadline to release and reinstate Bazoum - the democratically elected President - who has described himself as a hostage.
The crisis has raised tensions in the region and among Nigeriens abroad.
Ramatou Kané is from Niger but now lives in France.
"Today, we are in total uncertainty. We don't know, we don't know the motives of the coup leaders," she explained.
"We don't know their programme, we don't know their plans. We only know that they intend to take power. So, this gives rise to a great deal of concern."
Humanitarian groups in Niger have warned of “devastating effects” on the lives of over 4.4 million people needing aid.