Up to 25 people have been killed and others taken hostage in twin attacks on a military base and a uranium mine in Niger.
Niger's defence minister said 19 of the country's soldiers were killed and another 16 injured when a suicide bomber detonated a car bomb outside a barracks in Agadez.
At the same time least 13 people were injured and five suicide bombers killed in blasts at the Somaïr uranium mine in Arlit, about 800km north east of the capital Niamey and 100 miles from the barracks.
The attacks are believed to have been carried out by Islamic extremists based in neighbouring Mali.
Experts said that if they were, the twin attacks would be the single-most damaging operation militants from Mali had carried out since January when France launched a military intervention to oust them.
A member of the Niger government said responsibility for the attack had been claimed by the MUJWA militant group, an al Qaeda-linked West African militant group.
The attack on the barracks resulted in a fierce gunbattle. Security forces returned the town to calm but one attacker was still holding soldiers hostage, officials said.
Another spokesman, Abdou Labo, said in a press conference: "We have 19 dead in Agadez, 18 soldiers and a civilian," adding that four suicide bombers were killed in the blast.
"A fifth bomber has locked himself up in an office with several trainee officers as hostages," he added.
Niger government spokesman Marou Amadou said the mine had been "badly damaged" and had stopped production.
Areva, the French company that runs the mine, said in a statement that the mine had been the target of a terror attack at 5.30am local time and that 13 workers had been injured.
The statement said: "The group condemns this heinous attack against our personnel.
"Our thoughts are with the victims, their families, as well as all of our employees present in Niger.
"We express our solidarity with the government and the people of Niger during this shared ordeal."
The official ANP state news agency, citing unnamed sources, said the militants had entered Niger via lawless southern Libya, carrying explosive belts which they used in their attack.
In January, France sent several thousand troops to Niger's neighbour Mali to quell a growing threat from Islamists who had taken control of the Sahel region.
Figures linked to al Qaeda of the Islamic Maghreb (AQIM), an umbrella group for some of the Islamists in north Africa, threatened retaliation at the time.
MUJWA was part of a loose Islamist coalition which seized control of neighbouring north Mali last year before being ousted.
France has since started to withdraw its troops from Mali, but experts have said they fear its interests are still dangerously exposed in other parts of sub Saharan Africa.
In January, a regional al Qaeda commander claimed responsibility for a mass hostage-taking at the giant In Amenas gas plant in Algeria. At least 37 foreigners were killed in the attack, including five from the UK.