Although MTN believes there are no legal merits to Turkcell's claims and no legal basis for the U.S. court to consider them, the company has set up an independent investigation headed by British Supreme Court Judge Lord Hoffmann in a bid to resolve the matter outside the court.

MTN said Lord Hoffmann, who was born in South Africa, is widely regarded as a preeminent legal figure in the U.K. over the past 20 years and has a strong reputation for independence.

But Turkcell has declined to cooperate with the independent investigation that MTN has set up.

Last month, Dabengwa complained that MTN was finding it difficult to move money in and out of Iran and to import network equipment to improve service levels because of the sanctions from the U.S. and the E.U. over the country's nuclear program.