WASHINGTON (AP) - The State Department's warning that terrorists could strike at large holiday gatherings abroad is cause for caution but not panic, top U.S. officials said Sunday. Their comments came a day after the State Department cited "credible evidence" in warning of terrorist threats aimed at Americans traveling abroad for millennial celebrations. A worldwide caution issued by the department told U.S. citizens abroad to avoid large crowds and gatherings and to keep a low profile. The statement gave no details of the evidence and did not reveal which group may be the cause of the warning. But a senior U.S. official said the threat was linked to Osama bin Laden, who the U.S. government believes is the head of a terrorist network and is accused of involvement in the bombings last year of U.S. Embassies in Kenya and Tanzania.