The cross-border smuggling of illegal and regulated drugs is the greatest threat at the US-Canada international boundary, according to an internal Department of Homeland Security report released Thursday.

The "most common threat to U.S. public safety along the northern border continues to be the bidirectional flow of illicit drugs," the Northern Border Threat Analysis Report stated.

Cocaine and methamphetamine are smuggled from Mexico through the U.S. and into Canada, while smaller quantities of fentanyl, marijuana, and ecstasy are the most popular drugs flowing south from Canada into the U.S.

"To avoid detection by U.S. and Canadian law enforcement, transnational criminal organizations (TCOs) continually adapt their drug production, smuggling methods, and routes. The topography along mountainous parts of the northern border is occasionally exploited by smugglers flying private aircraft at low altitude to evade radar detection, but there are no reports to suggest that the tactic is employed on a large scale," the report stated.

Although drug smuggling remains a consistent problem at the northern border, DHS said terrain, weather, and distance help limit people from illegally entering the U.S. from Canada at remote spots.

Fewer than 800 people have illegally crossed from Canada into the U.S. annually over the past five years, compared to hundreds of thousands apprehended at the U.S.-Mexico border in that same time period.

"The large volume of legitimate travel across the northern border and the long stretches of difficult terrain between ports of entry (POEs) provide potential opportunities for individuals who may pose a national security risk to enter the United States undetected," DHS stated.

"However, encounters with individuals associated with transnational crime or terrorism remain infrequent, and sensor technology plays an important role in locations where full-time deployment of enforcement personnel is not practical. Known illegal crossings on the northern border conform to established migration patterns between large population centers," DHS added.