Mercedes team principal Toto Wolff says Nico Rosberg suffered a brake by wire failure at the start of the last lap which ultimately caused his turn two collision with team-mate Lewis Hamilton.

Battling for victory in the Austrian Grand Prix race leader Rosberg defended the inside line into turn two as Hamilton attacked around the outside.

The German driver missed his turn-in point which forced both Mercedes cars wide before Hamilton turned into the right-hander which saw the two collide.

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Rosberg lost his front wing while Hamilton recovered unscathed and went on to claim victory as his team-mate limped to the finish line to eventually take fourth place after being passed by Max Verstappen and Kimi Raikkonen.

Rosberg's result remains provisional as he is under investigation for the incident and driving a damaged car to the finish line.

Wolff has confirmed the F1 championship leader suffered a brake by wire failure - where he lost the full braking capability from his rear brakes - which caused him to run wide at turn two which sparked his collision with Hamilton.

"Nico had a brake-by-wire failure on the straight and defended very hard. Then seeing both cars nearly colliding is very upsetting," Wolff said on Sky Sports. "We had a marginal on the brakes if not to say completely over the brakes. We couldn't tell the drivers.

"It is racing but cars colliding it seems like d?j? vu when I'm speaking about colliding team-mates. It is absolutely not what we wanted and we just need to take the consequences now."

Wolff also explained the reasons behind Hamilton's strategy switch from a one to a two stop was to defend from Ferrari's attack with Sebastian Vettel which ended in spectacular style when the German's badly worn right rear tyre expired on the home straight on lap 26.

"We left Lewis out because we thought the one-stop was the quicker strategy," he said. "He was the car leading on track so he had the better strategy.

"We saw Ferrari tried to do the same and had the consequences of it with Sebastian and his tyre failure. When we realised we had to convert it to a two-stop that is where the problems started for Lewis."