Sebastian Vettel crashed out of the German Grand Prix when he was leading with only 16 laps to go

Ferrari's Sebastian Vettel says he is his own "biggest enemy" in his title fight with Lewis Hamilton this year.

Vettel, who is 30 points behind the Mercedes driver heading into this weekend's Singapore Grand Prix, has made a number of errors this season.

He said: "The biggest enemy is me. If we have something to play with, we have all the chances to do it in our way."

Hamilton added that he believed maintaining his advantage over the German was "going to be very tough".

Vettel was asked whether he could now not afford to lose any more points, following high-profile errors in the Azerbaijan, French, German and Italian Grands Prix that cost him more than 60 points in total.

"It is pretty straightforward," he replied. "He is ahead at the moment so he is the one to beat. But we have all the chances and how much they could be better by now is a different question.

"We still have a very, very good chance and we will be our first enemy, not him as a person and them as a team, we need to look after ourselves and if we do that we have a good chance to win races and things look good."

Vettel said his "worst" error had been when he crashed out of the lead in a late-race rain shower in Germany, which Hamilton went on to win.

"Most important is I know what happened and can explain it," he said. "Then everyone is free to have their views.

"I am not too bothered. I am generally looking forward and not focusing on what we could all have done differently to avoid what happened."

Vettel added he was optimistic of a strong weekend on the demanding Marina Bay street circuit in Singapore, which has traditionally been something of a bogey circuit for Mercedes.

Lewis Hamilton has won three of the past five races and holds a 30-point lead over Vettel in the drivers' championship

But Hamilton said he had "hope" that would not prove to be the case this weekend: "I can hope. That is probably the most powerful thing us as humans hold.

"It is going to be very tough these next races, still a lot of points available, Ferrari have had the upper hand performance-wise but as a team we have out-performed them.

"I am hopeful we can do it more but we come here, it is a downforce circuit and Ferrari should have the upper hand. But a lot of work has been going on at the factory and maybe we will be closer than in past years.

"There are still a lot points available. The approach is exactly the same as it has been all season. We do expect some difficult races ahead. Ferrari have been ahead of us the last few races and keeping ahead of them is going to be tough."