Sebastian Vettel has warned against writing Ferrari off in their battle for F1 supremacy with Mercedes, despite their season suffering more setbacks at the Russian GP.

The Scuderia have shown flashes of Mercedes-challenging form in 2016 but their start to the season has been blighted by unreliability and errors from the team and drivers.

Sochi has proved the scene of more frustration with Vettel's second-fastest qualifying time on Saturday cancelled out by a five-place grid penalty for a gearbox change.

In any case, Ferrari qualified 0.7 seconds adrift of Mercedes polesitter Nico Rosberg - their biggest deficit since March's Melbourne season-opener.

But despite suggestions that the Scuderia are not getting any closer to their rivals, Vettel insists the situation is better than it seems - even if the challenge of toppling Mercedes remains a difficult one.

"It's only three and a half races," Vettel stressed. "We had quite a trip so far with not everything going according to plan. We could have won the first race with things going a little bit differently, so overall it's not so bad.

Reaction from the top three drivers after qualifying in Russia Reaction from the top three drivers after qualifying in Russia

"We have shown great pace, especially on Sunday, and that's where you get the points. We know we have to work, and we are pushing very hard, but it's not so easy.

"Mercedes is doing a great job. Those two guys driving the cars are doing a good job, so it's a difficult team to beat.

"It's not a kindergarten, it's for grown-ups, and therefore the challenge is tough but we want to be the best so we need to be ready to tackle the best. So far we are very optimistic that we can turn it around."

The penalised four-time champion has to fight his way back through from seventh in Sunday's race, but is optimistic the SF16-H has the pace to do so.

"When you qualify second, that's where you sort of belong," he said. "With the penalty we start a bit further back, and I think we are quicker than those cars [Ferrari have fallen behind] so we have a good chance to make progress. But it's never easy."

Having already spent more development tokens than their rivals improving their engine for 2016, Ferrari used three more ahead of this weekend in a bid to aid performance and reliability.

Ferrari's Sebastian Vettel narrowly avoids colliding into the Mercedes of Lewis Hamilton in the pitlane during P3 in Sochi Ferrari's Sebastian Vettel narrowly avoids colliding into the Mercedes of Lewis Hamilton in the pitlane during P3 in Sochi

Raikkonen, however, denied the team expected more from the upgrade.

"It's working as we expect," the Finn said. "We know it's not a massive thing, it's small improvements here and there, with the car and the whole package.

Rosberg: Ferrari aren't close

"We always take it, but it's not going to make a big, big difference. People are very interested in it, but we put new parts on all the time. It's a normal thing."

The Finn blamed weekend-long tyre problems and mistakes on his Q3 laps for his failure to out-qualify Valtteri Bottas, a result which means Williams rather than Ferrari occupy the front-row slot vacated by the penalised Vettel.