WASHINGTON (AP) _ Threats have been made against federal buildings in the Washington area and some public tours have been halted, federal officials said today.

A Pentagon spokesman, Bryan Whitman, said Washington's largest federal building went on ``heightened alert status'' after the FBI warned Wednesday evening of ``possible terrorist activity aimed at installations in the National Capital Region.''

Whitman gave no further details, but callers were being told Pentagon tours have been canceled for today and Friday.

The heightened state of alert means that security personnel were screening passes for those entering the building more closely and might conduct random searches of packages and briefcases. Access to the building could also be restricted, Whitman said.

Justice Department spokesman Bert Brandenburg said unscheduled, informal tours of some buildings had been halted. He declined to provide specifics on the nature of the threats or which buildings may be involved. The FBI refused to comment.