The FBI's terror watch list contains roughly 900,000 records, a bureau spokesman said Thursday, confirming an earlier estimate by the American Civil Liberties Union.

Earlier this week, FBI spokesman Chad Kolton had indicated the database contained records on 300,000 individuals.

"That [information] was a little more dated than I thought," Kolton said Thursday.

Those records, however, connect to about 450,000 individuals, the spokesman said. The spokesman stressed that records may be aliases, nicknames or other differing data on a single individual.

Separate reported birthdates for the same individual would be stored as separate records, according to Kolton.

Ninety-five percent of the individuals in the database are not U.S. persons, the spokesman said.

The National Counterterrorism Center, which is responsible for maintaining watch list entries for individuals known or suspected to have ties to foreign terrorist groups, said earlier this week their list contained 500,000 records on roughly 400,000 people.

The NCTC list forms the basis of the FBI's list.  The bureau adds records connected to individuals believed to be terrorists who have no ties to foreign groups.

Asked about the apparent discrepancy in records between the NCTC list and the FBI's list, Kolton said it was likely because of differences in how the different systems count discrete records.