Nigeria’s Senate approved on Wednesday a report largely exonerating South African telecoms company MTN Group Ltd’s Nigerian unit, after the business was accused of illegally repatriating $14 billion to its parent.

But the Senate report also asked Nigeria’s central bank to sanction Stanbic IBTC Bank “for improper documentations in respect of capital repatriation and loan repayments” on behalf of MTN.

Parliament’s upper house agreed in September last year to investigate whether Africa’s biggest telecoms firm unlawfully repatriated $13.92 billion from Nigeria – its most lucrative market which generates a third of its revenue – between 2006 and 2016.

A spokesman for MTN said: “We welcome the report. We will study it in more detail. As we’ve placed on record previously, we have always insisted that our actions have been compliant with the law in this regard.”

Stanbic IBTC did not immediately respond to an email requesting comment.

The senate investigation did not receive proof of collusion to contravene Nigeria’s foreign exchange laws, according to the report.

“There was evidence of massive capital outflow but that fact alone is not conclusive that a crime has been committed,” the report said.

As for the Central Bank of Nigeria, the senate committee said its failure to properly regulate foreign exchange should be condemned.

The bank should propose amendments to current regulation to foster economic growth and improve Nigeria’s foreign currency inflows, said the report.

In July the Senate had rejected an earlier version of the report, asking for further work to be undertaken.