"There was an explosion in front of the military base at Agadez," Defence Minister Mahamadou Karidjo told AFP, calling it a car bomb attack.
"The attackers have been neutralised," he said, adding: "They are 'redskins'" -- a reference to members of the country's Tuareg and Arab groups.
Around the same time, an explosive-rigged four-by-four blew up at an Areva site to the north, injuring some at the scene, the employee said.
"A man in military uniform driving a four-by-four packed with explosives mixed in with the Somair workers and blew up his vehicle in front of the power station at the uranium treatment facility," the employee told AFP.
"Company managers told us the suicide bomber was killed in the explosion."
The attacks are the first of their kind in Niger, an impoverished west African country that has sent troops into neighbouring Mali as part of a regional military operation against Islamist fighters who had taken over the north of the country.