A NASA unmanned drone takes off from Wallops Island, Va. during a hurricane on Sept. 10, 2013. Drones fly over tropical storms and hurricanes to monitor weather conditions. Saul Loeb/AFP/Getty Images

The Federal Aviation Administration announced on Monday that six states will develop test sites for drones, a critical next step for the march of the unmanned aircraft into U.S. skies.

Alaska, Nevada, New York, North Dakota, Texas and Virginia will host the research sites, the agency said.

Drones are mainly used by the military, but local governments, businesses, farmers and others are making plans to join the market. Many universities are starting or expanding drone programs.

"These test sites will give us valuable information about how best to ensure the safe introduction of this advanced technology into our nation's skies," Transportation Secretary Anthony Foxx said in a statement.

The FAA does not allow commercial use of drones, but it is working to develop operational guidelines by the end of 2015, although officials concede the project may take longer than expected. The FAA projects some 7,500 commercial drones could be aloft within five years of getting widespread access to American airspace.

Amazon CEO Jeff Bezos announced Dec. 2 that the company plans to deliver packages by drone within four to five years assuming the FAA’s 2015 regulations allow such activity.