Guillermo Del Toro has pulled out of directing the two-part film version of The Hobbit for New Line and MGM.

Del Toro and Hobbit executive producer Peter Jackson announced the move on Sunday on the Tolkien fan site The One Ring. They said Del Toro will continue to co-write the films’ screenplays, based on the novel by J R R Tolkien, with Jackson and Fran Walsh.

Because of uncertainty about MGM’s future the films have not yet been given a formal green light, though the first has been slated for release - by New Line parent Warner in North America and by MGM internationally - in December 2012, with the second due to follow in December 2013.

In the announcement, Del Toro said: “In light of ongoing delays in the setting of a start date for filming The Hobbit, I am faced with the hardest decision of my life. After nearly two years of living, breathing and designing a world as rich as Tolkien’s Middle Earth, I must, with great regret, take leave from helming these wonderful pictures.

“I remain grateful to Peter, Fran and Philippa Boyens, New Line and Warner Brothers and to all my crew in New Zealand,” the director went on. “I’ve been privileged to work in one of the greatest countries on earth with some of the best people ever in our craft and my life will be forever changed. The blessings have been plenty, but the mounting pressures of conflicting schedules have overwhelmed the time slot originally allocated for the project.”

Jackson, who directed the massively successful Tolkien-based Lord of the Rings trilogy for New Line, added: “We feel very sad to see Guillermo leave The Hobbit, but he has kept us fully in the loop and we understand how the protracted development time on these two films, due to reasons beyond anyone’s control - has compromised his commitment to other long term projects. The bottom line is that Guillermo just didn’t feel he could commit six years to living in New Zealand, exclusively making these films, when his original commitment was for three years.”