South African officials on Friday hit back at US accusations that a sanctioned Russian ship had picked up weapons from a naval base near Cape Town late last year, a move investors feared could lead Washington to impose sanctions.

The US ambassador to South Africa said on Thursday he was confident that a Russian ship uploaded weapons from the Simon's Town naval base in December, suggesting the incident was not in line with Pretoria's professed neutrality in the Ukraine conflict.

President Cyril Ramaphosa's office said on Thursday that an inquiry led by a retired judge would look into the allegation. On Friday, a Minister responsible for arms control and a foreign ministry spokesman said the country had not approved any arms shipment to Russia in December.

"We didn't approve any arms to Russia, ... it wasn't sanctioned or approved by us," Communications Minister Mondli Gungubele, who chaired the National Conventional Arms Control Committee (NCACC) when the alleged arms shipment to Russia took place, told 702 radio.

Clayson Monyela, a spokesman for South Africa's department of international relations and cooperation (DIRCO), wrote on Twitter that his department would speak to US ambassador Reuben Brigety over his remarks and that Foreign Minister Naledi Pandor would talk to US Secretary of State Antony Blinken later in the day.

Neither Gungubele nor Monyela said whether or not an unapproved shipment had left South Africa.

Brigety offered no evidence on the alleged arms shipment at a briefing with local journalists on Thursday.

'MYSTERIOUS' SHIP
The US Treasury added the vessel that docked in Simon's Town, "Lady R", to its sanctions list in May last year for alleged weapons shipments along with other Russian-flagged cargo ships.

Opposition members called on South Africa's government at the time to explain what the "mysterious" ship was doing at the naval base.

"Evidence suggests that over the last two nights there was unusual activity in the harbour with on-board cranes offloading cargo from the Russian commercial vessel onto trucks," said Kobus Marais, who heads the opposition Democratic Alliance's defence portfolio, in a statement on December 8, 2022.

There were also trucks transporting containers in and out of the naval base, which is common but not at night, said Marais, adding that the trucks were protected by armed personnel.

The furore over the alleged arms shipment has heaped added pressure on the rand currency, which was already being weighed down by concerns over a power crisis and struck an all-time low on Friday.

"These allegations, if proven true, will have a significant negative impact on the economy, and will most likely jeopardize our trade relations, in particular our continued access to US markets," business lobby group BUSA said on Friday.

South Africa is one of Russia's most important allies on a continent divided over its February 2022 invasion of Ukraine, but says it is impartial on the conflict and has abstained from voting on UN resolutions on the war.

Washington has repeatedly warned countries against providing material support to Russia, cautioning that those who do may be denied access to US markets.

During a briefing on Thursday, US State Department deputy spokesperson Vedant Patel did not repeat the allegation that arms had been loaded onto the vessel.

He said Washington had serious concerns about the docking of the ship at a South African naval port and had raised those concerns directly with South African officials.

South Africa's defence department said on Friday it would give its side of the story to the government's inquiry.