The Secretary of the Homeland Security Department says a warning to airlines that terrorists could try to hide explosives in shoes was a routine advisory issued in response to the latest intelligence.

Secretary Jeh Johnson made limited comments on the threat during a news conference at Los Angeles International Airport Thursday. Johnson had toured the airport's security operations and planned to meet later with law enforcement at the Joint Regional Intelligence Center.

Johnson says shoe bomb threats have been around for years but the agency will sometimes update advisories or modify procedures to ensure vigilance.

A U.S. intelligence official told the AP that DHS released a notice to airlines reiterating that liquids, shoes and certain cosmetics were of concern. The warning was focused on international flights into the United States.