But authorities kept a high alert as investigators looked for proof of a plot possibly timed to disrupt events planned Sunday in Washington or New York.
Since late Wednesday, counterterrorism officials have chased a tip that al-Qaida may have sent three men to the U.S. on a mission to detonate a car bomb in either city. At least two of those men could be U.S. citizens, according to the tip.
No intelligence supported that tip as of Saturday, and officials continued to question the validity of the initial information.
While such tips are common among intelligence agencies, this one received more attention, and government officials chose to speak publicly about it, because of the connection to the anniversary of the worst terrorist attack in U.S. history.
Al-Qaida long has hoped to strike again on the anniversary.
At the FBI field office in Washington, assistant director James McJunkin described the tip and the response as routine. The U.S. already had bolstered security nationwide before the upcoming anniversary and anticipated an increase in tips.