<p>Passengers travelling to the United States from countries whose citizens do not need visas must register online with the US government at least 72 hours before departure, in the latest measure to strengthen American security.</p>
<p>The new rule is expected to be announced on Tuesday by MichaelChertoff, the Homeland Security secretary, and take effect in January 2009.</p>
<p>European companies last year expressed concern after the Homeland Security department floated the idea of requiring passengers to register 48 hours in advance, believing it could complicate last-minute business travel. Although the new rule requires 72 hours advance registration, it will be valid for multiple entries over a two-year period.</p>