Last month, the House of Representatives launched a probe into whether Nigeria can reduce the fine, which had originally amounted to $5.2 billion. In December, telecoms regulator NCC cut the fine to $3.9 billion.
The probe has hindered efforts by MTN to launch new talks aimed at getting the fine reduced further.
“As soon as the ongoing (parliamentary) investigations are concluded we will sit down with them (MTN),” communications minister Adebayo Shittu told reporters.
The House launched its investigation after MTN angered lawmakers by snubbing an invitation to its Nigeria Chief Executive Ferdi Moolman to appear at the telecoms committee, according to MPs.
MTN offered in March to pay $1.5 billion, according to a document seen by Reuters. And it dropped a legal case against the regulator as the first step in its efforts to reach an out of court settlement.
Last year, Nigeria imposed a deadline on mobile operators to cut off unregistered SIM cards, which MTN missed, amid fears the lines were being used by criminal gangs, including militant Islamist group Boko Haram.