Red Bull boss Christian Horner is looking to close the gap on Williams and Ferrari as the Formula 1 season moves to Europe.

The former constructors' champions have struggled for reliability since the start of the season and are languishing in fourth place in the 2015 standings.

However, Horner believes that the European segment of the campaign, which beginswitht next weekend's Spanish Grand Prix, represents an opportunity to make up some ground.

"Our target is to keep improving the car," Horner is quoted by F1i as saying. "After a difficult start last year we bounced back from pre-season testing to the first race and we want to try and make a big step forward in the next few races to put Williams and maybe even Ferrari under a bit of pressure.

"The team has been used to winning over the last few years and it's tough when you're not running at the front where that's where you're used to being. But the great thing here is that everyone is using it as a motivation to get back there. Everyone has got their head down, everybody's working incredibly hard and we can see progress in many areas.

"I think in this two week period to re-group and Renault to have done plenty of running on their dynos and iron out some of the issues they've had, has been very timely and hopefully we can use that to great effect in Barcelona next week."

Red Bull picked up three Grand Prix wins last season on their way to second place in the constructors' championship behind Mercedes.