CAPE TOWN, South Africa — South African President Cyril Ramaphosa has appointed a judge to oversee an inquiry into allegations that the country supplied arms to Russia on a ship that docked secretly at a naval base in December.

The allegations were made this month by the United States ambassador to South Africa, who said he was sure weapons and ammunition were loaded onto the Russian-flagged cargo ship Lady R when it docked at the Simon’s Town naval base near Cape Town late last year.

Ambassador Reuben Brigety indicated that the U.S. had intelligence to sustain the allegation.

South Africa has denied there was any government-sanctioned deal to provide weapons to Russia, although it hasn’t ruled out that an unofficial transaction took place involving another entity.

Judge P.M.D. Mojapelo, a former Supreme Court of Appeal judge, was appointed chairman of a three-member panel to investigate the incident. A lawyer and a former minister of justice were also appointed.

The panel has six weeks to complete its investigations and another two weeks from then to provide a report to Ramaphosa, the president’s office said.

South Africa could be in breach of international law and its own laws regarding weapons sales if it is found to have supplied arms to Moscow for the war in Ukraine.

South African Defense Minister Thandi Modise has refused to release cargo documents related to the visit by the Lady R after requests by opposition parties, saying they are classified. However, Modise said  she will release them to the inquiry.