Four men were arrested in Paarl in the Western Cape on Monday in connection with the bombing of Automated Teller Machines (ATM), Western Cape police said.
Lt-Col Andrè Traut said the group were arrested at their Mbekweni home around 2.40am, in an "intelligence-driven operation".
The men, aged 21, 27, 33 and 37, were found with commercial explosives, two illegal firearms and SA police service uniforms.
Their white VW minibus was confiscated.
Traut said the investigation was at a sensitive stage. He could not say how many bombings the group was linked to and whether further arrests were expected.
At least 20 ATMs had been blown up in the province since the beginning of the year.