Published: Mar 17, 2011 5:23 PM EDT
Updated: Mar 17, 2011 2:28 PM EDT

WASHINGTON- The Department of Homeland Security is screening passengers and cargo entering the United States from Japan for "even a blip of radiation."

Homeland Security Secretary Janet Napolitano said Thursday that no harmful levels of radiation have reached the U.S. since the nuclear crisis in Japan sparked by last week's devastating earthquake and tsunami.

Customs and Border Protection, which monitors ports, routinely screens passengers and cargo for radiation. Agents have been advised this week to pay particular attention to arrivals from Japan.

Napolitano said the screening of passengers and cargo is being done "in an exercise of caution."

The agency handles more than half a million radiation alarms a year, though most are related to medical procedures.

(Copyright 2011 by The Associated Press. All Rights Reserved.)