Peter Jackson has revealed that there is a legal block to his return to Middle-earth.

The filmmaker said that the Tolkien estate controls the film rights to JRR Tolkien's other works, and would have to cooperate in order for more films to be made.

"It's a legal thing," said Jackson at a press conference for The Hobbit: The Battle of the Five Armies (via The Hollywood Reporter).

"The Tolkien estate owns the writings of Professor Tolkien - The Hobbit and the Lord of the Rings were sold by Professor Tolkien the late '60s... the film rights.

"But they are the only two works of his that have been sold. So without the cooperation of the Tolkien estate, there can't be more films."

Tolkien's son and literary editor Christopher Tolkien and the estate have been critical of Jackson's films, saying that they "eviscerated" Lord of the Rings and accusing New Line Cinema of refusing to deliver their share of the profits.

Ian McKellen recently hinted that the third and final Hobbit film might not mark the end of the cinematic adventures in Middle-earth.

Tolkien's other books include The Silmarillion and Unfinished Tales.

The Hobbit: The Battle of the Five Armies will open in UK cinemas on December 12 and in the US on December 17.

He's just being greedy. His father sold the film rights so the deal was made a long time ago. Though if he's smart he could make a lot of money if he does have film rights for his dad's other books.