McLaren technical director James Key has praised Renault's progress with their power unit.

The French manufacturer has had a tricky season with reliability, including four engine-related retirements across both McLaren and the works team in the opening three races.

Those issues have eased since however, and now the work on improving performance, which has been a main weakness throughout the V6 hybrid era, is being felt.

"I have to say they’ve made some really good steps forward this year with their power unit," Key, who joined from Toro Rosso earlier this year, was quoted by F1i.com

"It’s been the best I’ve ever seen Renault have in terms of a performance step, and we can see that as well which is really encouraging.

"It’s a pleasure to work with them again. I think it’s the third time in a row!"

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Also now forging a relationship with Renault is McLaren's new team boss Andreas Seidl, who took over in his role at last month's Spanish Grand Prix.

"I think we have a great relationship with Renault," said the former head of Porsche's LMP1 program in the WEC.

"With Cyril [Abiteboul] and the guys from Viry, we have quite an open relationship.

"I’m pretty happy with the step Renault has also made from last year to this year in terms of power.

"We’re very happy with this partnership, but I think at the same time it is important for us to focus on ourselves and the work we have to do in Woking, because there is still a big gap compared to where we want to be as a team, and that’s my main focus."