(Bloomberg) -- Transnet SOC Ltd., South Africa’s state-owned ports and freight-rail company, said it had identified the source of the problem that forced the company to halt operations at its container ports.

Container terminals aren’t operating because of the malfunction in its computer network, though its rail, pipeline and engineering units are working as normal, the company said in a statement on Thursday. On Friday the company said it had identified the source of the problem, which the government has referred to as a cyber attack, and was working to minimize the impact. It didn’t disclose details.

The disruption prompted the company to manually conduct ports and rail operations, including at container and auto terminals at East London and Gqeberha, while exports of citrus fruits from South Africa -- the biggest seller of the fruit after Spain -- came to a grinding halt. Transnet operates sub-Saharan Africa’s largest port in Durban, and Richards Bay, the biggest single-site terminal for bulk shipments.

“We cannot export anything at the moment because the operations are at a standstill,” said Mitchell Brooke, development manager at the Citrus Growers Association. “That’s a big problem, a big challenge for us because we are sitting at the peak of our season and we can’t get product onto the market.”

Transnet’s website remained offline Friday afternoon. Transnet is prioritizing the export of reefer containers, which carry time sensitive cargo, via the Durban port due to the citrus season nearing its peak.

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Transnet said it has started loading two export-bound vessels and would soon embark on filling so-called reefer containers. The utility didn’t say when its operations would be back to normal.

The disruption is the second in about a week. Transnet declared force majeure on its Natcor line, which links the east coast city of Durban with the towns of Port Shepstone, Kroonstad, Richards Bay and the main economic hub of Gauteng, because of riots in parts of the country earlier this month.

The authorities are investigating “whether the cyber attack on Transnet is linked to the unrest,” acting Minister in the Presidency Khumbudzo Ntshavheni told reporters in Pretoria Thursday afternoon. “Currently we are treating it as an unrelated event.”

The United National Transport Union urged President Cyril Ramaphosa to instruct law-enforcement agencies to take “decisive action to protect Transnet” from sabotage, vandalism and criminality.

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