Islamist militants detonated car bombs within an hour of each other early Thursday morning in the Nigerien cities of Argadez and Arlit, which lie about 1,000 kilometers (621 miles) northeast of the capital city Niamey.
At least 20 soldiers were killed when the first bomb exploded on a military base in Argadez. The defense ministry indicated that at least 15 troops had been injured in the attack.
"The situation is under control and the search for the other attackers is under way," Defense Minister Mahamadou Karidjo told reporters. "There will be a 72-hour period of national mourning starting from today."
The second attack occurred at the Somair uranium mine in Arlit - about 240 kilometers apart northwest of Argadez - but only the suicide bombers died in the blast. French owner, Areva, said that over a dozen employees sustained injuries.
Islamist extremist groups, Movement for Oneness and Jihad in West Africa, or MUJAO, claimed responsibility for the attacks.
"Thanks to Allah, we have carried out two operations against the enemies of Islam in Niger," MUJAO spokesman Abu Walid Sahraoui told news agency AFP. "We attacked France and Niger for its cooperation with France in the war against sharia [law]."
Earlier this year, Niger sent troops to provide ground support to a French-led military operation tasked with ending Islamist control over northern Mali. Movement for Oneness, which has links to al Qaeda, and MUJAO were among the groups uprooted from the country in the counterinsurgency.
France condemned Thursday's attacks, which were unprecedented in Niger.
French Foreign Ministry spokesperson Philippe Lalliot said France pledged its "full solidarity with the Nigerien authorities in the fight against terrorist groups."
kms/jm (AP, AFP, dpa)