NIAMEY, March 17 (Reuters) - Niger's lower house of parliament voted unanimously on Friday to investigate accusations that President Mahamadou Issoufou's former chief of staff improperly participated in the state mining company's purchase of 5.5 million pounds of uranium.
A Nigerien newspaper published documents last month showing a bank transfer in November 2011 for $320 million from an account belonging to state miner Sopamin to an account controlled by an offshore company called Optima Energy.
The bank transfer was signed by Issoufou's chief of staff at the time and current finance minister, Hassoumi Massaoudou, who lawmakers have said had no authority to do so.
Local media has dubbed the affair "uraniumgate".
At a news conference last month, Massaoudou acknowledged signing the bank transfer but said his involvement in a series of transactions involving the uranium rights, ending in its sale by Sopamin to French state-owned nuclear company Areva , ultimately earned the state a profit.
He also denied suggestions by some lawmakers that some uranium could have been clandestinely sold in the process.
Reuters was unable to contact Optima, whose address on the bank transfer published by the Nigerien newspaper was listed in Lebanon. Areva did not immediately respond to a request for comment.
Niger is one of the world's top producers of uranium but ranks at the bottom of the U.N. Human Development Index out of 188 countries.
The commission of inquiry will have 45 days to conduct its investigation and will be composed of 10 deputies, lawmakers said.
(Reporting By Boureima Balima; Writing by Aaron Ross; Editing by Toni Reinhold)