The US ambassador to South Africa has accused the country of providing weapons and ammunition to Russia for its war in Ukraine via a cargo ship that docked secretly at a naval base near Cape Town for three days in December.
Ambassador Reuben Brigety said the US was certain the equipment was loaded onto the Russian vessel at the Simon's Town naval base and then transported to Russia, according to reports of his comments from multiple South African news outlets.
The country's president Cyril Ramaphosa said an investigation was under way.
When asked in parliament about the weapons and ammunition, the president replied that "the matter is being looked into, and in time we will be able to speak about it".
He declined to comment further, citing the need for an investigation to play out.
Mr Brigety was quoted as saying at a press conference in Pretoria, that "among the things the US noted" was the docking of a cargo ship in the Simon's Town naval base between 6 and 8 December last year - which he was "confident" was loaded with weapons and ammunition "as it made its way back to Russia".
The South African government, a key partner for the US in Africa, has stated numerous times it has a neutral position on the war in Ukraine.
In a statement issued later on Thursday, Mr Ramaphosa's office acknowledged a Russian ship named the Lady R docked in South Africa, but the office did not say where or what the purpose of the stop was.
The statement criticised the ambassador for going public and said there was an agreement that US intelligence services would provide whatever evidence they have to aid South Africa's investigation.
The Lady R and a Russian company tied to it, Transmorflot LLC, were sanctioned by the US last year following Russia’s invasion of Ukraine for being involved in the transportation of military equipment and weapons.
Ammunition supplies have become a problem for Russia in the war.
The leader of the Russian military company Wagner complained last week about his mercenary soldiers in Ukraine allegedly dealing with dire shortages.
Recent displays of South Africa's closeness to Russia have opened the country to accusations that it has effectively taken Moscow's side.
It hosted Russia's foreign minister Sergei Lavrov for talks in January, giving him a platform to blame the West for the war in Ukraine.
Weeks later, South Africa allowed warships from the Russian and Chinese navies to perform drills off its east coast.