Mercedes and Honda have stopped short of joining Max Verstappen in accusing Ferrari of "cheating" with its 2019 power unit.

In Austin, amid suspicions about Ferrari's huge power advantage, Red Bull-Honda requested a clarification from the FIA about fuel flow measurements.

Suddenly, and coincidentally, Ferrari's major engine advantage seemed to vanish.

"I have already discussed the data," Mercedes team boss Toto Wolff said. "Ferrari's top speed was completely different to the several previous races.

"But I don't know if that was due to the FIA directive, or some other problems. We don't know what Ferrari is doing, obviously," he added.

With a similar explanation is Honda's technical director Toyoharu Tanabe.

"If you look purely at the speed, the gap to Ferrari was smaller than in previous races. That is clear," the Japanese is quoted by Formel1.de.

"But we do not know if that is only because of the engine or also because of the chassis," he added.

Tanabe thinks the situation will become clearer in the next few weeks.

"We need the data from Brazil and Abu Dhabi," he said. "Then we will know more."