Team boss Toto Wolff has urged Mercedes to match Ferrari's recent gains in engine performance, and says he is not willing to accept that the Italian manufacturer has taken the upper hand in terms of power output.

Mercedes dominated the first three seasons under the current turbo hybrid regulations, but in the past two years Ferrari has made steady progress to close the gap. Evidence from recent races suggests Ferrari is now ahead in terms of engine performance, giving its drivers a distinct advantage on the straights at the last three rounds.

It is not yet clear how Ferrari has unlocked so much extra performance in such a small amount of time, but Wolff says he will not be satisfied until his team has come up with a response.

"We are not living with anything," he said. "I believe that it's nice again to be in a situation that you're the challenger and since 2013 we haven't been the challenger anymore.

"It's so difficult to set the benchmark, you're basically running around with a cross on your back. Now we know what the level of performance is with the Ferrari, you see it every day on track, and that is something which we are very eager and we are very motivated to achieve.

"We are not going on a rest until we have done that."

Mercedes sits ten points clear of Ferrari in the race for the 2018 constructors' championship. Charles Coates/Getty Images)

But Wolff admits his team is still not sure how Ferrari has unlocked so much extra power from the same set of regulations all manufacturer have been racing under since the start of 2014.

"It's very complex and not straightforward at all. Because of the maturity of these regulations, it's very difficult to extract more performance without harming reliability. So every experiment you do that potentially adds performance needs to be validated against reliability.

"At the end, a DNF is going to kill you in the championship much more than the ultimate last tenth of performance. It's very complex to extract more performance in the level that we need to be sufficient, but it's a challenging target."

Both Mercedes and Ferrari have one major engine upgrade still to come, which is expected to debut at one of the next two rounds in either Spa or Monza. Asked if he really thought Mercedes could match Ferrari, Wolff added: "Well we are going to. Andy Cowell [Mercedes' engine boss] and his troops, including the chassis integration team around it, will leave no stone unturned in order to match that.

"We would rather go up in flame than not match the performance."

One option could be delaying the introduction of Mercedes' next upgrade in order to spend more time on development.

"We will see what can be achieved, and what needs to be achieved, and at the moment we are in an interesting phase on the third engine and we are trying to extrapolate how much performance gains we can find until Spa or Monza.

"Only once we know that number we will be able to decide whether we need to postpone or do something else."