MTN Group may have illegally moved more than the previously claimed US$14bn out of Nigeria, a lawmaker said, citing early findings from an investigation into the allegation by international forensic experts.

“We have realised from preliminary investigations that it is actually outrageously higher than” the original figure, Dino Melaye, the senator who raised the allegation last month, told reporters in the capital, Abuja, on Wednesday.

Accountants and lawyers are also involved in the probe and are examining documents dating back 16 years, said senator Rafiu Ibrahim, chairman of the committee on banking, insurance and other financial institutions that is leading the inquiry.

MTN, Africa’s biggest wireless carrier by sales, has denied the claims. An investigative hearing in presence of the company, the central bank and four lenders is expected to be held on Thursday.

The investigation is taking place about four months after MTN agreed to pay a 330bn naira ($1,1bn; R14,1bn) fine in cash to the Nigerian government and list its local unit on the country’s stock exchange after about eight months of negotiations.

That penalty was imposed for missing a deadline to disconnect 5,1m customers unregistered in the country, which is battling an Islamist insurgency.

The shares declined by 2,3% to R107,50 as of 10.04am in Johannesburg. The stock has fallen by more than 43% since the fine was first reported a year ago, allowing crosstown rival Vodacom Group to overtake the company in terms of market valuation. — (c) 2016 Bloomberg LP