WASHINGTON (Reuters) – The Pentagon has given more than 130 U.S. military bases across the United States the green light to shoot down private and commercial drones that could endanger aviation safety or pose other threats.

The number of uncrewed aircraft in U.S. skies has zoomed in recent years and continues to increase rapidly – along with concern among U.S. and private-sector officials that dangerous or even hostile drones could get too close to places like military bases, airports and sports stadiums.

While the specific actions that the U.S. military can take against drones are classified, they include destroying or seizing private and commercial drones that pose a threat, Pentagon spokesman Navy Captain Jeff Davis told reporters on Monday.

The classified guidelines were distributed early last month. The Pentagon sent out unclassified guidance on how to communicate the policy to communities on Friday.

“The increase of commercial and private drones in the United States has raised our concerns with regards to the safety and security of our installations, aviation safety and the safety of people,” Davis said.

In April, flights of nearly all drones over 133 U.S. military facilities were banned due to security concerns.

Drones have become popular as toys and with hobbyists, and have commercial uses such as aerial photography. Amazon.com Inc <AMZN.O> and Alphabet Inc’s Google unit <GOOGL.O> have been exploring the use of drones to deliver goods ordered online.

The FAA estimated the commercial drone fleet would grow from 42,000 at the end of 2016 to about 442,000 aircraft by 2021. The FAA said there could be as many as 1.6 million commercial drones in use by 2021.

(Reporting by Idrees Ali; Editing by Jonathan Oatis)