7 May 2013 BBC Africa
A Nigerian warplane involved in operations against militant Islamists in Mali has crashed in Niger, killing two pilots, the army has said.
These are the first casualties Nigeria has suffered after deploying troops in January to fight the militants.
Mechanical failure was likely to have caused the fighter jet to crash near Mali's border while it was on a non-combat mission, reports say.
International forces uses Niger as an airbase for operations in Mali.
France has started to withdraw some of its 4,500 troops from Mali, hoping that African forces will take over the campaign to fight the militants.
The UN Security Council passed a resolution in April to incorporate the 6,000-strong African force in Mali into a UN force numbering 11,200.
Chad and Nigeria form the bulk of the African troops in Mali.
Nigerian Air Force spokesman Commodore Yusuf Anas told Reuters news agency that an investigation was underway to establish the cause of the crash.
"They were on a normal routine flight about 60km (37 miles) west of Niamey when something happened," he told Reuters.
Army sources in Niger ruled out the possibility that the jet had been shot at, saying it was not in "enemy territory".
French and African troops have driven the militants out of northern cities and towns in Mali - including Timbuktu and Gao - since combat operations started in January.
But some fighters have retreated to desert hideouts in the vast region, from where they launch isolated attacks against French and Malian forces.
The al-Qaeda-linked militants took advantage of a coup in Mali in March 2012 to extend their control across the north of Mali.
France intervened, saying Mali could become a "terrorist state" that threatened global security.