WASHINGTON (AP) -- Government officials say at least two of the men suspected of being involved in a possible al-Qaida attack to coincide with the 10th anniversary of the 9/11 attacks are believed to be U.S. citizens or have U.S. traveling documents.

The officials say the information comes from a single source and it has not been confirmed.

One official says the would-be attackers' primary goal is to set off a car bomb, but if that proves impossible, they have been ordered to find some other way to cause violence. The tipster says the would-be attackers are of Arab descent and may speak Arabic as well as English.

The officials say the tips reached the CIA by way of a long-term source in the Afghanistan-Pakistan region who has proven reliable in the past. They spoke on condition of anonymity to discuss the investigation.

(Copyright 2011 by The Associated Press. All Rights Reserved.)