MotoGP World Championship leader Casey Stoner has extended his contract with Ducati until the end of the 2008 season, Australian media reported on Wednesday.

The 21-year-old Australian extended his lead at the top of the standings on Sunday with an impressive victory at Barcelona's Circuit de Catalunya, his fourth victory in his first full season with the Italian outfit.

"We plan for Casey to be with Ducati in 2008," team boss Livio Suppo was quoted as saying by Australian Associated Press.

The Italian team has exercised an option on Stoner in advance of a September deadline. Stoner's business manager and father Colin confirmed the contract extension and said he was looking to secure a longer-term relationship with Ducati.

"Casey has renewed with Ducati for 2008 and we are already talking about the future and I envisage that by the end of this season we will have something concrete for 2009 and 2010," Colin Stoner said.

"Both parties are happy to continue. We don't want to go anywhere and Ducati don't want Casey to go anywhere."

Stoner leads the world championship by 14 points after the victory in Barcelona, the seventh race in the 17-round calendar.

He is aiming to become Australia's first world champion in motorcycling's top category since Michael Doohan completed the last of his five victories in 1998.