Kimi Raikkonen says Ferrari's performance deficit to Mercedes changes at each circuit and differing conditions but concedes his team must continue to improve to catch its rivals.

The Ferrari driver was forced to settle for fourth place in the Grand Prix of Europe at Baku after a convincing drive in isolation was dampened by being passed by Sergio Perez late on - but the Finn would have had to take fourth place regardless after picking up a five-second post-race time penalty for crossing the white line at pit entry.

After seeing team-mate Sebastian Vettel take second place but lack the pace to challenge winner Nico Rosberg, Raikkonen says Ferrari's recent gains on Mercedes are impacted by different circuit characteristics and conditions.

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The Baku circuit looked largely to play against Ferrari with both drivers struggling for speed on Friday but a solid recovery gives Raikkonen confidence the gap is closing to Mercedes.

"If you take purely the result between the last couple of races, I'd say we were closer in Canada than here [Baku]," Raikkonen said. "But then it swaps between different circuits, different conditions.

"It was not the easiest weekend for us, we were struggling with a lot of things. In the end, we turned it around."

Raikkonen still feels Ferrari has a chunk of performance to make up to catch Mercedes outright but is optimistic these gains are in the pipeline.

"We have quite a bit of work to be done to be able to challenge them every race, every conditions, that it doesn't matter where we go that we can challenge them," he said. "It varies places, layouts, conditions. To be really comfortable and challenge them, we have things to improve."