Africa's largest mobile operator MTN says it is reviewing allegations that it paid protection money to militant Islamist groups in Afghanistan.The allegations, made in a legal complaint filed in a US federal court on Friday, say the firm violated US anti-terrorism laws.It was filed on behalf of families of US citizens killed in attacks in Afghanistan.Five other companies were also named in the filing.The complaint alleges MTN paid bribes to al-Qaida and the Taliban to avoid having to invest in inexpensive security for their transmission towers.The alleged payments helped finance a Taliban-led insurgency that led to the attacks in Afghanistan between 2009 and 2017, the accusations say.It is alleged that the money helped to provide "material support to known terrorist organisations," thus violating the anti-terrorism legislation.The South African telecommunications giant says it remains of the view that it conducts its business in a "responsible and compliant manner in all its territories".MTN is Africa's largest mobile operator and the eighth largest in the world, with more than 240 million subscribers.In 2015, the firm was fined more than $5bn (£3.8bn) by the Nigerian authorities for failing to cut off unregistered sim cards - a figure that was reduced to $1.7bn after a long legal dispute and the intervention of South Africa's then-President Jacob Zuma.In February, a former South African ambassador to Iran was arrested in the capital, Pretoria, on charges that he took a bribe to help MTN win a $31.6bn (£24bn) license to operate in Iran.