Pirelli left the Belgian Grand Prix insisting that its 2017 tyres are safe.
During the Spa weekend, alarming slow-motion footage showed the rear tyres of some cars vibrating so severely under acceleration that parts of the cars broke off.
F1's official tyre supplier launched an investigation.
Pirelli technical boss Mario Isola is quoted as saying by Auto Motor und Sport: "It only happened in two places - under acceleration in turns 1 and 19.
"Of course we saw the TV pictures, but we also saw data from some teams showing vibrations that we haven't seen before.
"But after inspecting the tyres we can say that everything is safe. The tyres do not rotate on the rims - we can see this from markings and the position of the valves."
The championship continues with the Italian Grand Prix on Sunday.
