ABUJA, March 24 (Reuters) - Nigeria's parliament has launched a probe into whether the telecoms regulator can reduce a fine slapped on South Africa's MTN for missing a deadline to disconnect unregistered SIM card users, a lawmaker said on Thursday.
The move might complicate efforts by Africa's biggest cell phone operator to reduce the fine, which had originally amounted to $5.2 billion.
In December, the telecoms regulator NCC reduced the fine to $3.9 billion, but on Wednesday lawmakers in the lower house of parliament said the original fine could not be altered unless the law was amended.
"For you to adjust the fine, you have to adjust the law, that is where I am finding difficulty," said Yakubu Dogara, speaker of the House of Representatives, according to parliament's minutes seen by Reuters on Thursday.
[READ: MTN in talks with Nigeria regulator to cut $3.9 bln fine and plan payment: Buhari]
The house launched a probe after lawmaker Ehiozuwa Agbonayinma asked, in a motion read out by Dogara, for the MTN fine to be more than tripled to $15.6 billion.
Agbonayinma also demanded that MTN face criminal charges, saying the firm's failure to disconnect users SIM cards had led to the death of some 10,000 Nigerians as criminals had used the unregistered cards, according to the motion.
MTN had angered the house by snubbing an invitation to its Nigeria Chief Executive Ferdi Moolman to appear at the telecoms committee, a lawmaker said.
Instead of sending Moolman, MTN issued a letter telling lawmakers "appropriate government agencies ... are in a position to furnish your committee with relevant information on this issue," lawmakers said, according to the minutes.
MTN said in a statement it was aware of "reports out of Nigeria about the fine" and was awaiting clarity from the West African nation's government.
The NCC could not immediately be reached for comment. Shares in MTN, which makes about 37 percent of its sales in Nigeria, were down 10 percent at 1450 GMT.
MTN earlier this month offered 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.
($1 = 199.0000 naira) (Reporting by Camillus Eboh, Felix Onuah, Ed Stoddard and Alexis Akwagyiram; Writing by Ulf Laessing; Editing by Mark Potter)