The terrorist threat to the United States has not abated despite government steps in the past year to tighten rules for people and goods that enter the United States, the nation's chief of homeland security said Wednesday. "The fact that we have not had a terrorist attack on this country in the last six years is not a cause for complacency or a time to celebrate," Michael Chertoff said Wednesday during a year-end speech. "The threat is not going away. The enemy has not lost interest. And if you have doubt about it, look at yesterday's reports about bombings in Algeria." Chertoff spoke a day after twin truck bombings by an affiliate of al-Qaida targeted UN offices and a government building in Algiers, killing at least 31 people.