The junta, which took power in a coup in July last year, has vowed to revamp rules regulating the mining of raw materials by foreign companies in what is the world's seventh-largest uranium producer.

In June, authorities withdrew Orano's permit to exploit one of the largest uranium deposits in the world, Imouraren, which holds an estimated 200,000 tonnes of the heavy metal.

Then, in late October, the French group suspended production by its local unit, Somair, in the northern Arlit region owing to what it termed increasingly difficult operating conditions and financial issues.

The company has also denounced the impossibility of exporting uranium since Niger's border with Benin was closed for what Niamey says are security reasons.

Orano holds a 63.4-percent stake in Somair while the share of the Nigerien state stands at 36.6 percent.

"For several months, Orano has been warning of the interference that the group has been suffering in the governance of Somair," the French group said in a statement.

"The decisions taken at the company's board meetings are no longer being applied and, as a result, Orano is today confirming that the Nigerien authorities have taken operational control" of Somair, it said.

The latest clash between the junta and Orano, majority owned by the French state, comes as Niger has downgraded links with former colonial power France and strengthened ties with new partners including Russia and Iran.

Last month, Nigerien Mining Minister Ousmane Abarchi invited Russian firms to invest in uranium and other natural resource production in his country.

- Financial situation 'worsening' -

Orano said Somair's board had decided on November 12 to suspend expenses related to production activities "in order to prioritise the payment of salaries and preserve the integrity of the industrial facilities".

But days later, a delegation of regime advisers visited Somair mines in Arlit to encourage work there to continue.

Orano said enforcement of the board's decision "is being deliberately prevented".

"The production expenses which continue to be incurred on the site are worsening the company's financial situation with every passing day," the statement said.

It added that "representatives of Niger" defended their position at a board meeting on Tuesday, "in particular confirming their refusal to export the production".

A total of 1,150 tonnes of uranium concentrate from 2023 and 2024 stocks -- the equivalent of nearly half of annual production in Arlit -- are being blocked, according to Orano. It is worth around 200 million euros ($210 million).

"Orano expresses its deepest regret regarding the evolving situation which is placing a heavy burden on the employees and local communities," the company said.

"Orano intends to defend its rights before the competent bodies and reaffirms its belief that only a united effort by all stakeholders to re-establish a stable and sustainable mode of operation can allow Somair to resume activities in peace."