The EU has suspended all security cooperation with Niger after the country's army took power in a coup.
It comes shortly after the US declared its "unflagging support" for ousted president Mohamed Bazoum - seen as a key Western ally in the fight against Islamist militants.
On Friday the head of the presidential guards unit Gen Abdourahmane Tchiani declared himself Niger's new leader.
He said insecurity, economic woes and corruption led him to seize power.
But there are now concerns in the West about which countries the new leader will align with.
Niger's neighbours, Burkina Faso and Mali, have both pivoted towards Russia since their own coups.
EU foreign policy chief Josep Borrell joined the US and France in refusing to recognise the coup leaders and said security cooperation and budgetary aid was being suspended indefinitely.
Also on Saturday France, the former colonial power which had moved its regional military headquarters to the country after being forced to leave Mali, said it had suspended all development aid and budgetary support.
Meanwhile the African Union called on the Niger army to return to base within 15 days.
On Friday evening US Secretary of State Antony Blinken warned those detaining Mr Bazoum - Niger's first elected leader to succeed another since independence in 1960 - that "hundreds of millions of dollars of assistance" was at risk.
However, the leader of Russia's Wagner mercenary group has reportedly described the coup as a triumph.
"What happened in Niger is nothing other than the struggle of the people of Niger with their colonisers," Yevgeny Prigozhin was quoted as saying on a Wagner-affiliated Telegram channel.
"With colonisers who are trying to foist their rules of life on them and their conditions and keep them in the state that Africa was in hundreds of years ago."
He added: "Today this is effectively gaining their independence."
The BBC has not been able to verify the authenticity of his reported comments.
Wagner is believed to have thousands of fighters in countries including the Central African Republic (CAR) and Mali, where it has lucrative business interests but also bolsters Russia's diplomatic and economic relations.
Wagner fighters have been accused of widespread human rights abuses in several African countries.
The more I read, the more I feel the whole world is turning to shit. Pretty much anything that happens in China. Russia's attack on Ukraine and basically everything it feels it can successfully attack. Populists (often pro-Russian ones) winning (or gaining support) en-masse across the western world, taking away people's rights. Military coups in western allied countries in Africa. Pretty much everything going on in the middle East.
Africa has been a monstrous mess since the colonialism times. Europeans committed many atrocities there and a lot of them carried on and are what we see today. Humanity has a lot of baggage and that's mostly where today's problems come from. It's not that the world is doing a 180. More like a 30 degree turn or 45 tops.
The world is always cyclical. There is always a return to conflict and friction. And given that the globalized world has shifted and mixed so many, I think we're definitely brewing some nice widespread instability which will, in time, give way to a new form of stability. Whether it'll better than what we have now is the main question. Seems unlikely, but it always does.
Ribbit