* Areva says 13 staff wounded at plant in Arlit
* Some 20 soldiers killed, 16 wounded in barracks attack
* Minister says MUJWA militant group claims responsibility
Islamist suicide bombers struck a barracks and a French-run uranium mine in Niger on Thursday, officials said, killing 20 people and wounding dozens in attacks that showed armed unrest spreading across West Africa.
In Agadez, the largest town in northern Niger, at least 20 soldiers were killed and 16 injured when suicide bombers attacked a barracks at dawn, Defence Minister Mahamadou Karidjo told state radio. Three Islamists were also killed.
After a fierce gunbattle, security forces returned the town to calm but one attacker was still holding soldiers hostage, military sources and local officials said.
Further north in Arlit, at least 14 civilians were injured and two Islamists killed in a car bomb attack at the Somair uranium mine operated by run by French nuclear group Areva , the minister said.
Niger officials said crushing and grinding units had been badly damaged at the Areva plant and uranium production had stopped.
Al Qaeda's north African wing AQIM took five French workers hostage in 2010 at the remote site, 1,200 km (750 miles) north of the capital Niamey.
Karidjo said responsibility for the attack had been claimed by the MUJWA militant group, a West African offshoot of AQIM. The group was part of a loose Islamist coalition which seized control of neighbouring north Mali last year before being ousted by a French-led offensive launched in January.
"The situation is under control and the search for the other attackers is under way," Karidjo told state radio. "There will be a 72-hour period of national mourning starting from today."
The suicide attacks were the first in Niger since the offensive in Mali drove Islamist groups there across borders into neighbouring Sahel states.
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.
Niger's army has deployed some 650 troops as part of a regional West African force in Mali. Islamist suicide bombers have carried out a spate of attacks there in recent months, including one on a Niger barracks this month.
In January, a regional al Qaeda commander claimed responsibility for a mass hostage-taking at the giant In Amenas gas plant in Algeria, in response to the French offensive in Mali. At least 37 foreigners were killed in the attack.
In Agadez, a suicide bomber drove a Toyota truck through the barrier of the town's military base at around 5.30 a.m. on Thursday and detonated his explosives when soldiers opened fire, military sources said.
Security forces returned the dusty, mud-brick town to calm after hours of gunbattles with Islamists, and then moved through the town to mop up any isolated militants.
"One of the attackers has taken two or three soldiers hostage and is holed up in a house. We have him surrounded," said one source.
Areva said in a statement issued in Paris that at least 13 members of staff had been wounded in the attack on its Somair mine, where AQIM had kidnapped five French staff in 2010.
Areva said security at the site was being handled by the Niger military. French sources said in January Paris planned to sent special forces to the area for extra protection.
"The group condemns this odious attack against its staff," Areva said. "We express our solidarity with the government and the people of Niger in this common trial."
Niger's armed forces have taken part in recent weeks in a joint operation against Boko Haram Islamists in the Nigerian town of Baga on the shore of Lake Chad, in which dozens of people were reported killed.
Nigeria again asked its northern neighbour for military aid this week, after President Goodluck Jonathan declared a state of emergency in three northern states and launched an offensive against Boko Haram insurgents.