South Africa’s MTN Group, Africa’s largest mobile operator, has disclosed that it is under investigation by the United States Department of Justice (DoJ) over its past activities in Iran and Afghanistan. The announcement comes at a time of heightened diplomatic tension between Washington and Pretoria.

In a statement released alongside its financial results, MTN confirmed that it had been made aware of a U.S. grand jury probe relating to its former Afghan subsidiary and its minority stake in the Iranian carrier, Irancell. “MTN is cooperating with the DoJ and voluntarily responding to requests for information,” the company said.

Grand juries typically decide whether to bring formal charges in cases and whether matters proceed to trial.

The telecom giant has also been named in a separate U.S. lawsuit filed by American veterans wounded in Iraq and Afghanistan, as well as relatives of soldiers killed in action. The plaintiffs allege that MTN supported anti-American militias through its participation in Irancell, claims the company firmly denies. MTN said it intends to file a motion to dismiss the case, stressing that it has not engaged in any wrongdoing.

MTN’s troubles over its Iran operations are not new. In 2006, it was selected ahead of Turkey’s Turkcell to acquire a 49 percent minority stake in Irancell, a decision that has since sparked a corruption lawsuit from Turkcell in South African courts.

The latest legal challenges come against the backdrop of strained relations between the U.S. and South Africa. Washington has criticized Pretoria for its close ties with Russia, its genocide case against Israel at the International Court of Justice, and its handling of domestic land issues, which former U.S. President Donald Trump claimed amounted to persecution of white farmers. Trump also imposed a 30 percent tariff on most South African exports, the highest such duty in sub-Saharan Africa.

For MTN, the unfolding investigations in the U.S. add to a complex web of legal and geopolitical challenges that could shape its international operations in the years ahead.