Red Bull driver Daniel Ricciardo admits that the Austrian team are off the pace after the opening four races of the Formula One season.

The former world champions have been plagued with reliability problems this season and are 136 points adrift of leaders Mercedes after just four of 19 races.

"I think at the moment we are not on the pace with Mercedes and Ferrari. They're our target for now, even Williams have been a bit quicker so far. So we need to crack into the top five for sure and then once we're there we will look towards the top three and obviously get back on the podium," said Australian Ricciardo.

Red Bull won four successive drivers' and constructors' titles with Renault engines from 2010 to 2013 but have been off the pace since the introduction last year of a new V6 turbo hybrid power unit.

Ricciardo is already on his fourth engine for the season out of an allocation of four, although teams are set to agree an increase to five, making grid penalties inevitable. Despite the problems, Ricciardo is optimistic that the team can turn their season around.

"We will have some aerodynamic updates in Barcelona and we're hoping for a bit more from the engine as well, a bit more power," said Ricciardo.

"I think these are the small steps that will keep getting us closer and closer," he said, pointing out how much Ferrari have improved since the end of last season.

"At the end of last season I think we were clearly in front of Ferrari but they've made a really big step in the off season so they've been the biggest movers so far, but for us it's good to see and we know a big step like that is possible," he said.

With 15 races still to come, Mercedes' non-executive chairman Niki Lauda warned against any complacency in the German team.

"The season is not finished. It's only the fourth race. Ferrari is very strong, there's no question about it and, as a racing team, you never think that nobody can catch you, then you make a big mistake," he said.