Guillermo Del Toro has quit as director of the two The Hobbit movies, but will still help write the screenplays for the Lord of the Rings prequels.

"In light of ongoing delays in the setting of a start date for filmingThe Hobbit I am faced with the hardest decision of my life," the Mexican filmmaker said in a press release.

"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."

Del Toro and producer Sir Peter Jackson said they remained committed to the films and would do everything they could to satisfy fans.

Del Toro said he would be first in line to see the finished films.

"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 told fan website TheOneRing.net: "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. Guillermo is one of the most remarkable creative spirits I’ve ever encountered and it has been a complete joy working with him."

The Hobbit films have been plagued by delays, and have not yet been greenlit by the studio, MGM, which is having financial troubles.

At a press conference last week, del Toro said: "It's not greenlit."

"That's categorical ... We've been caught in a very tangled negotiation ... There cannot be any start dates until the MGM situation gets resolved. They do hold a considerable portion of the rights.

"We have designed all the creatures. We've designed the sets and the wardrobe. We have done animatics and planned battles sequences ... We are very, very prepared for when it is finally triggered."

Jackson told TheOneRing.net that he would discuss options for a new director with MGM this week.

"We do not anticipate any delay or disruption to ongoing pre-production work," he said.

There have also been discussions about shooting the prequels, which are due to be released in 2012 and 2013, in 3D.