Niki Lauda has said that Sebastian Vettel's first-lap retirement at Sochi means Mercedes is still in the dark about Ferrari's true pace.

On the face of it, notwithstanding worries about reliability, reigning world champions Mercedes utterly dominated in terms of pace in Russia.

Ferrari's Kimi Raikkonen finished third on Sunday, while Vettel did not even complete a lap.

"I would have preferred that [Daniil] Kvyat had not taken him out, then we would be able to assess exactly how good Sebastian's engine update really is and how much closer he has got to Mercedes," Mercedes team chairman Lauda told the German broadcaster Sky.

"The logic of the race is that Mercedes was three, four tenths quicker in the race than Kimi."

Lauda said that Ferrari team boss Maurizio Arrivabene congratulated him after the Russian Grand Prix for Mercedes's latest one-two finish.

"He really is a fair sportsman," said Lauda, "but I confessed to him at the same time that we were lucky with Lewis's loss of water, otherwise [Raikkonen] might have been one place higher.

"But we have a good relationship with Ferrari and I would do exactly the same in reverse."

Mercedes published an impassioned open letter to their fans on Wednesday, in reaction to suggestions that the team is deliberately sabotaging Lewis Hamilton's title campaign.

"And to the rest - the haters, the naysayers, the conspirators - if we can convince even half of you of what we really stand for, we'll consider that a battle well won," an excerpt reads.

The season continues with the Spanish Grand Prix on May 15.