WASHINGTON -- Nearly all air travelers entering the United States will be required to show passports beginning Jan. 23, including returning Americans and people from Canada and other nations in the Western Hemisphere.

The date was disclosed Tuesday by Homeland Security Secretary Michael Chertoff.

Until now, the department had not set a specific date for instituting the passport requirement for air travelers, though the start had been expected to be around the beginning of the year.

Currently, U.S. citizens returning from other countries in the hemisphere are not required to present passports but must show other proof of citizenship such as driver's licenses or birth certificates.

People from Canada, Bermuda -- and those from Mexico who enter the U.S. frequently and have special border-crossing cards -- have been allowed to use other forms of identification, including driver's licenses.