MTN Nigeria said on Saturday it is under investigation by the Nigerian anti graft agency over its listing last week, although it “has not been accused of any wrongdoing” by the Economic and Financial Crimes Commission, EFCC.

The listing of MTN Nigeria, a unit of South African telecoms firm MTN Group, made it the second-largest firm on the Nigerian Stock Exchange, and since then its share price has risen from 90 naira to 140 naira.

A spokesman for Nigeria’s financial crimes agency was not immediately available for comment, according to Reuters

“We received all regulatory approvals required to list our shares,” MTN Nigeria said in a statement. “We are co-operating fully with the authorities.”