Hakkinen retired from F1 in 2001

The 36-year-old Finn, who won F1 titles in 1998 and 1999 with McLaren, retired to spend more time with his son Hugo.

But he has accepted the offer to drive for Mercedes in touring cars.

"I have close ties to Mercedes and look forward to taking part in the Touring Car Championship next year. My target is obviously to win it," said Hakkinen.

During his 10-year McLaren career, Hakkinen won 20 Grands Prix and achieved 26 pole positions.

He had been linked with a move back into F1 in recent months, with Williams and BAR mentioned as possible destinations.

But he has opted for a new challenge in touring cars and will drive the AMG-Mercedes C-Class in 2005.

"After the end of my Formula One career in 2001, I soon realised that I was not ready to retire for good," he said.

"It was just the right moment that Mercedes-Benz offered me to test a DTM [Deutschen Tourenwagen Masters] car.

"I saw immediately that I still enjoy racing very much and during the test three weeks ago, my lap times were at the same level as those of the touring car specialists."