In an interview with Bloomberg News, Homeland Security Secretary John Kelly said that not only would the U.S. likely maintain a ban on certain electronic devices on airlines but that the ban could be expanded to include other devices and other modes of transportation due to an ongoing terrorist threat.

“It could be everywhere, frankly,” Kelly told the website. “The threat is real. There are any number of cells out there who could be doing their very best to figure out ways of beating our security.

“The United States still has the best security in the world,” Kelly continued. “It’s the hardest target to get to, but it’s also the target that they want to get to the most.”

As of now, the ban – issued in March by both U.S. and British officials – only affects travelers flying out of eight Middle Eastern countries. Kelly said that the ban was based on “some very serious intel” that showed that ISIS terrorists were working on a bomb that could be hidden within electronics only slightly larger than a cellphone.

“This thing could expand – and I’m looking at it three, four, five, six times a day,” Kelly said. “It is the thing that keeps me awake at night.”

DHS officials have said that the expanded ban could affect flights coming out of the United Kingdom. If implemented, it would probably resemble the one already in place for flights coming out of several countries in the Middle East and northern Africa. That policy requires travelers flying out of 10 major airports to place all electronics larger than a phone into their checked baggage. Currently, the ban includes laptops, larger gaming devices, e-readers, tablet computers, and more.

“Evaluated intelligence indicates that terrorist groups continue to target commercial aviation and are aggressively pursuing innovative methods to undertake their attacks, to include smuggling explosive devices in various consumer items,” said a senior administration official after the ban was introduced two months ago.

This is one of those situations where the implications are even more frightening than the specific threats. If ISIS and other Islamic terror groups have developed the technology to miniaturize their bombs to such an extent that even a Kindle could be used as a weapon of mass destruction, there may be no security ban in the world strong enough to prevent a tragedy. It’s another reminder that, even though the U.S. has gone a few months without coming face to face with a terror attack, our enemies are always waiting, always plotting, and always looking for the next opportunity to shed American blood.