The Revenue Service said Africa's biggest economy imported 417,000 tonnes of Iranian crude in February, a dramatic reversal of a declining trend seen since October, when it imported 467,000 tonnes.
South Africa has come under Western pressure to cut Iranian crude imports as part of sanctions designed to halt Tehran's suspected pursuit of nuclear weapons, although it has been unclear how diplomatically non-aligned Pretoria is responding.
Senior energy and foreign ministry officials directly contradicted each other last month as to the status of Iranian imports.
However, January trade and customs data showed Iranian crude imports at zero compared with a monthly average of $280 million last year.
Iran has been South Africa's biggest crude supplier, accounting for a quarter of its oil imports.
The biggest South African buyer of Iranian crude is Engen, majority-owned by Malaysian national oil company Petronas . Engen has not commented, but a Petronas source told Reuters last month Engen had stopped buying Iranian oil from March.
Petrochemicals group Sasol, which took 12,000 barrels of Iranian oil a day, says its has already found new suppliers but has not named them.
In January, trade figures showed a spike in imports from Saudi Arabia, Qatar and Ecuador, suggesting they were being used as alternative suppliers to Iran.
In February, Saudi Arabia was South Africa's biggest supplier, with 582,000 tonnes of crude, followed by Iran, Nigeria, Angola an Ecuador.