A U.S. federal judge has ruled that 20th Century Fox owns a copyright interest in Watchmen, which may jeopardize Warner Bros.'s plan to release the superhero movie in March.

Judge Gary Allen Feess issued the surprise ruling on Wednesday, Variety reported.

"Fox owns a copyright interest consisting of, at the very least, the right to distribute the Watchmen motion picture," the ruling said.

Judge Feess advised both Fox and Warner to consider either a settlement or an appeal.

Fox acquired rights to the Watchmen graphic adventure novel in the late 1980s for producer Lawrence Gordon. After spending more than $1 million US developing the project, it eventually dropped its plan to make a movie based on the work written by Alan Moore and illustrated by Dave Gibbons.

Gordon later carried out the project with Warner Bros. and Legendary Pictures. The movie, about the underside of life for superbeings, was directed by Zack Snyder and stars Patrick Wilson and Jackie Earle Haley. Its release is scheduled for March 6, 2009.

In February, Fox filed a suit to prevent Watchmen from being released. It argued that Gordon's option to acquire Fox's remaining interest in Watchmen was never exercised.

Warner spokesman Scott Rowe has declined to comment on the ruling.

The Wall Street Journal says the ruling in favour of Fox comes as a surprise, "given that the studio appeared to have dropped the project more than a decade ago and was not involved in producing the film."

With files from the Associated Press