"We continue to face one of the most challenging threat environments since 9/11, as foreign terrorist organizations exploit the internet to inspire, enable or direct individuals already here in the homeland to commit terrorist acts," reads the bulletin.
The National Terrorism Advisory System bulletin, which replaced the old color-coded system, is used to give the public and local law enforcement a summary about ongoing and potentially new terror threats.
"The current bulletin introduces unmanned aircraft systems as potential threats and highlights sustained concern regarding threats against commercial aviation and air cargo," said DHS acting press secretary Tyler Houlton in a statement.
There's been an "uptick in terrorist interest" in using unmanned aerial systems as weapons in the United States and other western countries, according to a senior DHS official.
These tactics have been used by terrorists on the battlefield, and the department wants to "guard against those tactics being exported to the west," said the official.
The official said that DHS wants to be "forward leaning" about seeing what terrorists are doing overseas and tactics they might adopt in the future.
Since the last bulletin, concerns about terrorist targeting aviation sector have grown, said the official.
"[T]errorists continue to target commercial aviation and air cargo, including with concealed explosives," reads the updated bulletin.
DHS has been implementing wide-ranging security measures for all airports and airlines that fly directly to the U.S. In June, the administration announced "enhanced screening" of passengers and their electronic devices, as well as "seen and unseen" security around the aircraft and inside the airport.
Terrorists still see "aviation as the crown jewel target," said former DHS Secretary John Kelly, now the president's cheif of staff, at the time of the announcement.
The measures, which are being rolled out in phases, are aimed at detecting concealed explosives, insider threats and identifying suspicious passengers.
Current acting DHS Secretary Elaine Duke has been urging countries to adopt these measures on all flights, not just those that are direct to the U.S., according to a DHS official.
The new bulletin also warns of the use of "poisons or toxins," which the DHS official says there has been increased chatter about in the terror realm.
The "big picture" is that the homeland security fight is shifting, said the senior DHS official. The department's response to the terror threat is adapting as ISIS is close to defeat in safe havens, but continues to have branches and affiliates around the world, according to DHS.
DHS is focused on the next phase of the fight, according to the senior DHS official.