A government spokesman said 19 soldiers were killed and more than a dozen injured in Agadez when a vehicle drove into a barracks and exploded just before dawn, The Wall Street Journal reported.
One person was killed and 14 others injured in an early-morning suicide attack on a mining operation in Arlit owned by uranium mining group Areva about 100 miles north of Agadez.
No group has taken responsibility for the attack, Voice of America reported.
Islamic militants in recent months have attacked French companies and groups after the European country led a military initiative in Mali against insurgents.
Agadez has been under consideration by the United States as a possible base for surveillance drones deployed to Niger earlier this year.