Lewis Hamilton: Mercedes driver confident he can catch Nico Rosberg

In four races this season, Hamilton has two second-place finishes, a third and seventh

Lewis Hamilton says he is looking at his difficult start to 2016 as a case of "glass half full" as he starts to try to close the points gap to Nico Rosberg.

The world champion is 43 points behind his Mercedes team-mate after a series of problems in the first four races and victories for the German in all of them.

Hamilton said eliminating the deficit will be a "big challenge" but added: "There's a lot more to come from us."

He said he was "confident" Mercedes would solve his reliability problems.

Hamilton has been afflicted by the same problem with the MGU-H - a part of the engine's hybrid system - in qualifying for the last two races.

In China four weeks ago it meant he had to start from the back and in the next race in Russia from 10th. He was up to second in Sochi and closing on Rosberg when his engine began to lose water pressure and he had to back off to ensure he reached the finish.

"We've had a hard time but the guys in the garage are doing a fantastic job and I'm really happy with how we've been working together," Hamilton said ahead of this weekend's Spanish Grand Prix.

"Every weekend, we've got the car into a great place set-up-wise - I just haven't been fully able to exploit it. So the glass is half full for me.

"There's a long way to go with 17 races left.

"The team has been on it 24/7 since returning from Russia so I'm confident they'll get to the bottom of the problems we've been having.

"I know I'm still quick. I've known that since day one in testing and, when I've had clean air and a damage-free car this season, I've shown it on track.

"I head to Spain confident of a good weekend."

Mercedes head of motorsport Toto Wolff admits it has not been "plain sailing" this season

Mercedes executive director (technical) Paddy Lowe said that solving the problem with the MGU-H was "the highest priority" for the team's weekend at the Circuit de Barcelona-Catalunya.

"The team has been working day and night to understand it and we're targeting a clean weekend all round," Lowe said.

Mercedes head of motorsport Toto Wolff said: "We are leading the constructors' championships by a good margin and our drivers hold the top two positions in the drivers' standings.

"So, realistically speaking, it's tough to ask for more.

"However, it has not been plain sailing and we have had problems that we are working hard to solve.

"We have rivals breathing down our necks who are relentless in their chase.

"The longer regulations remain stable, the harder it is to find extra performance.

"We are pushing the limits to ensure we remain competitive - but if you push the limits then at a certain stage you risk stepping over them."