AUSTIN, Texas (Reuters) - A U.S. military appeals court ruled on Monday that the trial of Major Nidal Hasan, accused of killing 13 people in a 2009 massacre at the Fort Hood base in Texas, can go ahead even though a dispute over whether his beard must be shaved has not been resolved.

The court martial of Hasan, who is Muslim, was to have begun last week but was delayed over the beard, which violates Army grooming regulations. The appeals court did not order him to be shaved but asked the judge in the case to reconsider the issue.

Hasan is accused of opening fire at a deployment center at Fort Hood, Texas, on November 5, 2009 and faces 13 counts of premeditated murder and 32 counts of attempted premeditated murder in the shooting at the sprawling Army base.

(Reporting by Karen Brooks; Editing by Greg McCune)