"The case does not seem to pose any immediate concerns about aviation security measures in Japan," he said.
Spokesman Keisuke Hamatani said officials at Kansai International Airport are investigating, but that airport security officials had not reported spotting any suspicious-looking passengers as described in media reports, or any suitcases containing the hazardous materials allegedly found in Harris' luggage.
Airport police said they do not believe the case constitutes illegal conduct under the Japanese domestic criminal code. But they said Japan may cooperate at the request of U.S. investigators.
Spagat reported from San Diego. Associated Press writers Rodrique Ngowi in Boston, Eric Talmadge and Mari Yamaguchi in Tokyo and Alicia A. Caldwell in Washington contributed to this report.