STORM2K

Washington (CNN) -- U.S. officials said Thursday evening they have "specific, credible but unconfirmed" information about a threat against the United States coinciding with the 10th anniversary of the September 11 terrorist attacks.

"We have received credible information very recently about a possible plot directed at the homeland that seems to be focused on New York and Washington, D.C.," a senior administration official told CNN Pentagon Correspondent Barbara Starr.

The official said the plot was believed to involve three individuals, including a U.S. citizen, who may have entered the United States. U.S. officials believed the threat was a vehicle laden with explosives, but "the intelligence picture is not completely formed," the official said. "Not enough is known about the potential operatives and their plotting."

Another source gave CNN conflicting information about possible details of the threat.

A senior law enforcement official involved in briefings about the matter told CNN Justice Department Producer Terry Frieden that his best information is that the three individuals had not yet entered the United States.

FAYETTEVILLE, N.C. -- Officials at Fort Bragg say an investigation is under way into the disappearance of nearly 14,000 rounds of ammunition at the Army base.

Staff Sgt. Joshua Ford, a spokesman for the 82nd Airborne Division, says the ammunition went missing from the 1st Brigade Combat Team at Fort Bragg.

The Fayetteville Observer reports that Ford believed the ammunition was taken overnight on Tuesday. The 1st Brigade team was placed on lockdown for a few hours Wednesday night while officials conducted a search.

The missing ammunition can be used in an M-4 or M-16 assault rifle.

Ford says the 82nd Airborne Division and military police are taking the matter seriously and that "any amount of ammunition that goes missing" has "got to be accounted for."