Sebastian Vettel is ignoring complaints about Ferrari's engine as questions over its legality continue.

2019 has seen the Italian team hold a large advantage over their rivals on the straights, something that has been attributed to both more power and less drag.

However, the dramatic difference in performance between qualifying and the race led to Mercedes and Red Bull calling for clarification on certain tricks which could offer Ferrari a single-lap boost.

A first directive from the FIA was given before the US Grand Prix and it just so happened that their recent surge was halted, as Charles Leclerc finished 50 seconds behind race winner Valtteri Bottas while Vettel retired.

That led some to suggest Ferrari had been found out.

“Should we have the strongest engine, which I don’t know the other manufacturers' power figures, that’s a great achievement by us, by our engine department," he responded to reporters in Sao Paulo on Thursday.

“For the last five years, we had Mercedes having the strongest engine, but now for a couple of months we are ahead and hopefully it stays like that for the next five years and I don’t care what people think or say."

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Asked though what would stop the speculation, the four-time champion added: “The best way to answer [critics] in a way is to probably go back to normal.

“We are not proud of how we performed in Austin on Sunday. After Saturday, nobody had the need to complain.

“Sunday I think we struggled probably with more than one thing, conditions, tyres, setup, which are things we need to work on, but calling it that far I think is not right. But again, live and let live."

Max Verstappen would infuriate Ferrari and the Italian media by suggesting their US slump was a result of no longer cheating and Vettel too was less than impressed.

“There is not much to say about it. I think that comment was very immature," he said. 

"I ignore it because it is irrelevant. We want to answer on the circuit. Austin was not a good weekend for us, especially the Sunday, but we work hard to keep up."