Pirelli has revealed its findings after investigating the cause of the tyre failures that led to high-speed accidents for Max Verstappen and Lance Stroll in the Azerbaijan GP.
After extensive analysis since the Baku race on June 6, F1's tyre supplier said the blowouts on the circuit's main straight were caused by a "circumferential break on the inner sidewall" on the left-rear hard compound, which was related to the "running conditions of the tyre".
Pirelli concluded there were no quality defects or signs of fatigue from the tyre, which in both instances had been used for more than 25 laps. Tyres used by other cars in the race for similar stint lengths were also examined.
Pirelli made clear Red Bull and Aston Martin correctly followed the mandated starting parameters regarding minimum tyre pressure and maximum blanket temperature.
Revised protocols have now been agreed with the FIA and will be introduced from the French GP this weekend.
"The process established that there was no production or quality defect on any of the tyres; nor was there any sign of fatigue or delamination," read a Pirelli statement.
"The causes of the two left-rear tyre failures on the Aston Martin and Red Bull cars have been clearly identified. In each case, this was down to a circumferential break on the inner sidewall, which can be related to the running conditions of the tyre, in spite of the prescribed starting parameters (minimum pressure and maximum blanket temperature) having been followed.
"As a result of this analysis, Pirelli have submitted their report to the FIA and the teams. The FIA and Pirelli have agreed a new set of the protocols, including an upgraded technical directive already distributed, for monitoring operating conditions during a race weekend and they will consider any other appropriate actions."
In a subsequent statement, Red Bull said: "We have worked closely with Pirelli and the FIA during their investigation into Max's tyre failure on lap 47 of the Azerbaijan Grand Prix and can confirm that no car fault was found.
"We adhered to Pirelli's tyre parameters at all times and will continue to follow their guidance.
"We are grateful that following the weekend's high speed impacts no drivers were injured."
Red Bull's Verstappen was heading for race victory and an extended championship lead over Lewis Hamilton when his left-rear tyre let go with six laps remaining in the race. Stroll's Aston Martin was pitched into a high-speed spin into the barriers on lap 29.
Pirelli boss Mario Isola had said that initial post-race assessments at the track suggested debris may have been the cause of the blowouts. However, the fuller investigation back at Pirelli's Milan base subsequently ruled that out.