Thousands of tiny unmanned aircraft or drones flying into civilian airspace over the United States can pose a security threat as they may be difficult to monitor in the long run and some craft may fall into enemy hands, security analysts say.

Although debate over the use of surveillance drones, centers on civil liberties and individuals' rights, a much greater risk of hostile drones entering U.S. airspace undetected isn't being considered, says a UPI report. 

The Federation Aviation Administration said up to 30,000 drones could be in airspace shared with airliners carrying passengers.

There is risk that terrorists will attempt to penetrate the drone network with unpredictable consequences for the safety of the set-up as well as citizens, the report said.  

U.S. defense and security forces deployed drones of varying sizes in Afghanistan and Iraq. The CIA's armed Predator drone program targeted al-Qaida leaders but officials said smaller drones were deployed outside U.S. diplomatic areas in Iraq to monitor the safety of U.S. officials during their movements within the country.