WASHINGTON — The number of people barred from buying guns because of mental health problems has more than doubled since the Virginia Tech shootings earlier this year, the Justice Department said Thursday.

The increase follows stepped-up reporting to a federal database used to screen the backgrounds of potential gun-buyers.

Attorney General Michael Mukasey was to announce the increase at an afternoon speech in Park City, Utah. The number of people identified in the database as having mental problems grew from 174,863 three months after the April 16 Virginia Tech shootings to 393,957 this month.

"Instant background checks are essential to keeping guns out of the wrong hands, while still protecting the privacy of our citizens," Mukasey said in prepared comments prepared for delivery to the National Association of Attorneys General.

"But as we learned in the tragedy at Virginia Tech, the checks must be accurate and complete to be effective," Mukasey said. "We're making progress, and I hope that even more states will submit this information so that the national instant background check system can be maximally effective."

People are included in the federal database only after courts or other lawful authorities have found them to have mental health problems, Justice Department officials said. Currently, 28 states submit names to the mental health database, and the federal government cannot force the other 22 to follow suit.