Although U.S. authorities say there is no credible intelligence regarding a specific threat against such hospitals, the bulletin said there have been persistent reports of "suspicious activity" at medical facilities throughout the United States.
That includes "possible reconnaissance activities" this year at unspecified military medical facilities in Bethesda, Md., and Aurora, Colo., the bulletin said. Even though later investigation of these two incidents uncovered no links to terrorism, the bulletin urges vigilance at VA hospitals on the part of police and security personnel.
"These facilities may be considered attractive targets due to their association with the military and a perception that such an attack may be more successful than an attack against traditional military targets, which generally maintain a more robust security posture," the bulletin says.
Bethesda, located just outside Washington, is home of the National Naval Medical Center, which is across the street from the sprawling National Institutes of Health. Aurora, located just east of Denver, is home to the former Fitzsimons Army Medical Center, now being redeveloped into a civilian medical school.
The Department of Veterans Affairs operates 163 hospitals in the United States, with at least one in each of the 48 contiguous states as well as in the District of Columbia and Puerto Rico. There are also hundreds of VA clinics and nursing homes.
The bulletin was circulated among law enforcement and security personnel nationwide Thursday. The Associated Press obtained a copy Friday.
Earlier this month, the FBI warned that al Qaeda might attempt to attack military recruitment centers, which are also less tightly guarded than other military facilities.
The new bulletin repeats a number of previously released indicators of possible terrorist surveillance. These include unusual interest in security measures or access points of buildings; operatives possibly disguised as "panhandlers, shoe shiners, food or flower vendors"; discreet use of video cameras in areas not frequented by tourists; and individuals seen observing security drills or procedures.
U.S. officials have repeatedly warned that al Qaeda is likely to attempt an attack inside the United States before the Nov. 2 election. Security is extraordinarily tight for next week's Republican National Convention in New York, where captured al Qaeda documents indicated planning for possible strikes against financial interests in New York and Newark, N.J.
The FBI has also previously warned that al Qaeda might attempt to attack lightly guarded targets such as apartment buildings and hotels.