The FBI and the Department of Homeland Security (search) are warning that terrorists may try to use helicopters and limousines as weapons, according to newly-released bulletins sent to law enforcement agencies throughout the country.
The warnings, which include concerns about a range of rental vehicles that could conceal powerful bombs as well as storage facilities, were issued Friday night and were obtained by FOX News.
The bulletins urge extra vigilance by people who operate car and truck rental businesses and those who handle airport security. The FBI repeated the government's concern that Al Qaeda intends to attack the United States in the next few months, prior to the Nov. 2 election.
The FBI and DHS said that Al Qaeda (search) remains committed to using aircraft for future attacks within the United States.
"Al Qaeda operatives are known to have considered conducting an attack against U.S. interests using a helicopter packed with explosives," the bulletin states. "Although there is no credible specific evidence supporting the use of helicopters, in aerial attacks within the United States, the threat cannot be discounted."
"Al Qaeda has apparently considered the use of helicopters as an alternative to recruiting operatives for fixed-wing aircraft operations," the bulletin states. "Terrorists may view helicopters as an attractive weapon due to their maneuverability and non-threatening appearance when flying at low altitudes in urban environments."
The bulletin also points out that Al Qaeda may be targeting key financial institutions.
"By extension, any densely-populated urban area of symbolic, economic or financial importance could pose a targeting opportunity in a strategic helicopter attack," the bulletin states.
The FBI and DHS noted that possible attack scenarios could include Al Qaeda operatives finding vulnerabilities in security procedures to hijack commercial helicopter flights.
"Operatives may also contract a flight from a charter or tour service to facilitate a hijacking," the bulletin says. "Helicopters could be used in suicide attacks against high profile ground targets or to attack the public in open areas, including parades and sporting events, with explosives carried on board to increase the destructive effects."
But the warning did not deter tourists who boarded helicopters for sightseeing tours of the New York area on Monday.
"We're all here and we're all together," said Gisele Dorte of Martinique, who boarded a Liberty Helicopter Tours chopper with her family.
Another bulletin says that terrorists could use a variety of rental vehicles to conceal powerful bombs, including limousines that have a larger storage capacity than rental cars.
In addition, the FBI said, limousines might be able to gain access to locations in a building — such as a parking garage — that would be denied to other vehicles because "they often convey an impression of authority or prestige."
Still, White House officials are optimistic that the recent arrests of suspected terrorists and the seizure of detailed surveillance of financial buildings has undermined plans to attack the United States.
Officials also suggested in television talk shows Sunday that some of the potential plots uncovered in the past week may have been part of a broader effort to strike the country before the November election.
"I certainly think that by our actions now that we have disrupted it," Frances Fragos Townsend, President Bush's homeland security adviser, said on "Fox News Sunday." "The question is, have we disrupted all of it or a part of it? And we're working through an investigation to uncover that."
In cooperation with U.S. intelligence agencies, authorities in Pakistan and Britain have detained suspected Al Qaeda operatives, while computer files uncovered in Pakistan contained surveillance information of five prominent financial sites in New York, Washington and Newark, N.J. The administration issued a terror alert based on that information.
Besides the financial sites, counterterrorism officials have said other places have been mentioned as possible targets. Asked whether they included the Capitol and members of Congress, Townsend replied: "Yes, in the past and as part of this continuing threat stream."
Included in information obtained on three laptop computers and 51 discs seized in a July 24 raid in Pakistan were details of how Al Qaeda operatives thought of using speed boats and divers to carry out attacks in New York harbor before the November election, Time magazine reported, quoted an unidentified U.S. law enforcement official.
A senior Pakistani Al Qaeda operative who formerly ran one of the terror group's training camps in Afghanistan was arrested in the United Arab Emirates and has been handed over to Pakistani officials.
Condoleezza Rice, Bush's national security adviser, defended the administration's decision to issue the terror warnings and tighten security in three cities, even though some of the surveillance intelligence on which the government acted dates from four years ago. Some have questioned whether the warnings were politically motivated.
"The idea that you would somehow play politics with the security of the American people, that you would not go out and warn if you have casing reports on buildings that are highly specific -- are you really supposed to not tell?" Rice said.
In order to act quickly on recommendations from the commission that investigated the Sept. 11 attacks, House Democratic leader Nancy Pelosi of California has urged Speaker Dennis Hastert, R-Ill., to call a special session of Congress. Hastert said House committees are working on the recommendations, with hearings this week.
"I hope that when we come back in September and October, we have the recommendations and we can move forward," he said. Legislation to overhaul intelligence agencies could pass this year, he added.
Pelosi has called House Democrats to a meeting Tuesday with commission members.
FOX News' Anna Stolley and the Associated Press contributed to this report.