Tandja ally concedes defeat in Niger poll
* Oumarou says will not challenge results
* Issoufou's win paves way for civilian rule
* Issoufou's party plans $12 bln investment during term
NIAMEY, March 17 (Reuters) - Niger presidential challenger Seyni Oumarou conceded defeat in a poll run-off late on Wednesday, removing the last major hurdle to a smooth transition to civilian rule in the uranium-producing West African state.
Provisional results of Saturday's election showed opposition leader Mahamadou Issoufou won with some 58 percent against 42 percent for Oumarou, a party ally of ex-president Mamadou Tandja who was ousted by soldiers last year for outstaying his term.
"I have decided ... against making a request to the constitutional council to annul the results," Oumarou told reporters before heading to Issoufou's residence to congratulate him in person.
A desert nation whose uranium riches have drawn billions of dollars of investment, mainly from French nuclear giant Areva, Niger remains one of the world's poorest countries, dogged by corruption and instability.
It has suffered repeated coups since independence in 1960 and has recently faced attacks by al Qaeda-linked militants who have targeted mining staff and other expatriates for ransom.
Issoufou, 58, promised during the campaign to raise about six trillion CFA francs ($12.7 billion) during his five-year term to invest in agriculture, infrastructure, energy and other projects to create about 50,000 jobs annually.
Earlier this week Niger announced it had doubled to 650 million barrels its estimate of oil reserves being developed at the Agadem block with China National Petroleum Corporation (CNPC). (Reporting by Abdoulaye Massalaatchi; Writing by Mark John; Editing by David Lewis and Jon Hemming)
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