The U.S. Federal Bureau of Investigation controls a fleet of airplanes equipped with technology that could be used to keep tabs on people from above, according to a new report from The Associated Press.

The FBI's surveillance planes are supposedly used only to support the agency's operations on the ground, the AP reports. But in recent months, news outlets (namely the Washington Post and the AP) tracked some of these planes closely and found they made repeated trips over nearly a dozen U.S. cities.

Now the AP, as well as many people reading the AP's report, are asking questions about what, exactly, all these planes are up to.

Here's what we know so far: [Flying Saucers to Mind Control: 7 Declassified Military & CIA Secrets]

The FBI's aerial missions are nothing new

The FBI has been using small aircraft to support its ground operations (for example, tracking suspects) since at least the 1980s, according to AP's report, which also states that the planes are owned and operated by front companies. These companies were created to protect the safety of pilots and to ensure that suspects on the ground don't identify the planes as belonging to law enforcement agencies, FBI officials told the AP.

Officials also pointed out that the FBI's aviation program is not a secret. (Documents related to the program's budget, with portions censored, are available online.)

Other government agencies — including the Drug Enforcement Administration (DEA) and the U.S. Marshals Service — also have planes at their disposal that are registered to fake companies. Law enforcement officials told the AP that these companies were created with the approval of Justice Department lawyers and that the Federal Aviation Administration is aware of the practice.

The tech on board some of these planes is new

Some of the FBI planes that have flown over major U.S. cities in recent months were equipped with surveillance technologies, according to the AP. These technologies include video cameras and devices that may be able to capture private data from cellphones.

The AP report does not specify which technologies these planes have onboard, but one of the devices mentioned is a called a "cell-site simulator," which can trick a cellphone into recognizing a plane as a cell tower. The device can trigger cellphones on the ground to share their identification numbers (i.e., the 10-digit number associated with the phone). And the cameras onboard the planes can capture high-quality video from a distance, even at night, according to the AP.

It's not clear how this technology is being used

There are many details about the FBI's aviation program that are not clear. The agency's public reports on the program are censored and, as the AP points out, information about surveillance flights is left out of court documents related to FBI cases. The FBI also did not disclose how many planes are operating under the program.

Other missing details include how the tech onboard the planes is being used. The cell-site simulators — which are also found aboard planes operated by the U.S. Marshals Service — are only used in limited situations, according to FBI officials, but they did not explain exactly what those situations are. The FBI has recently begun obtaining court orders to use some of the more advanced technologies mentioned in the AP's report (such as the high-quality video cameras and cell-site simulators).

Although the Justice Department recently published a "privacy policy" that covers the FBI and other agencies' use of drones and unmanned aircraft, the drone rules don't apply to the piloted planes used in the FBI aviation program, according to the AP. However, FBI officials said that manned flights do comply with established Justice Department rules.

However, just what those rules are is still something of a mystery. All that is known publically is that the regulations limit the types of surveillance equipment that the FBI can use onboard the planes, as well as the justifications for using this equipment.

More than 100 flights tracked by AP

It's still not clear what the FBI's planes are doing overhead or what information they are collecting about whom. What is clear is that the planes have been spotted above at least 11 states, including the District of Columbia. The AP said it tracked more than 100 FBI-operated flights over major cities, including Boston, Chicago, Dallas, Houston, Minneapolis, Phoenix, Seattle, as well as cities in Southern California.

The planes, most of which were Cessna 182T Skylane aircraft, circled large buildings and other sites for extended periods, according to the AP. These sites included the Ronald Reagan Washington National Airport and the Mall of America in Bloomington, Minnesota. The planes typically flew at low speeds, in a counterclockwise direction several miles wide, at an altitude of about 5,000 feet (1,524 meters), according to the AP.

Although the AP report does not say what these planes may have been doing, it does note that a company that makes camera equipment like that seen on these planes recommends that pilots fly slowly counterclockwise to capture footage.

Follow Elizabeth Palermo @techEpalermo. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.