President Trump has declared that the U.S. is engaged in an "armed conflict" with drug cartels, previously labelled as terrorist organisations, in a confidential notice to Congress this week.

The covert announcement was initially reported by The New York Times and sent to several congressional committees. According to international law, during an armed conflict, a country can legally kill enemy combatants even if they pose no immediate threat, detain them indefinitely without trials, and prosecute them in military courts, reports the Express US.

This news follows recent unexplained U.S. military strikes on boats in the Caribbean Sea, which resulted in 17 fatalities. The administration has yet to provide evidence that those aboard were members of a drug cartel. The news emerges after Trump shares video as he blows up another ‘drug boat’ leaving 3 dead.

The Trump administration has justified them as acts of self-defence, alleging that the casualties were transporting drugs for cartels into the U.S..

In a report by The Times, the notice - classified as controlled but unclassified information - cites a statute requiring reports to lawmakers about hostilities involving U.S. armed forces. It also suggests that the military's recent attacks in the Caribbean are part of an ongoing conflict rather than isolated acts of self-defence.

The notice further alleges that Trump has "determined" that cartels involved in drug smuggling are "nonstate armed groups" whose actions "constitute an armed attack against the United States."

The Trump administration did not specify any particular cartels it is in armed conflict with within the notice, nor what criteria it is using to determine whether certain suspects are collaborating with these organisations.

The notice described the three victims of the most recent attack on a boat on Sept. 15, as "unlawful combatants."

"The vessel was assessed by the U.S. intelligence community to be affiliated with a designated terrorist organization and, at the time, engaged in trafficking illicit drugs, which could ultimately be used to kill Americans," the notice said. "This strike resulted in the destruction of the vessel, the illicit narcotics, and the death of approximately three unlawful combatants.

"Based upon the cumulative effects of these hostile acts against the citizens and interests of the United States and friendly foreign nations, the president determined that the United States is in a noninternational armed conflict with these designated terrorist organizations," the notice read.