Niger has barred the local operations director of the French nuclear company Areva from returning to the country after a visit abroad.
Areva is the world's largest maker of nuclear reactors
The authorities offered no explanation for the ban imposed on Dominique Pin.
Areva, which mines uranium in northern Niger, has rejected accusations that it is linked to rebel activity.
Some weeks ago, an Areva security adviser was expelled amid local media claims that the country was supporting the Niger Movement for Justice rebels.
Areva condemned the measures against Mr Pin.
"Nothing that Dominique Pin has done justifies such action," a company official told the news agency AFP.
"The accusations made out against Areva are without any foundation," the official added.
Areva is the world's largest manufacturer of nuclear reactors.
The company has been operating in Niger for 40 years and is the country's biggest private employer, according to AFP.