The Trump administration is framing its boat strikes against drug cartels in the Caribbean in part as a collective self-defense effort on behalf of US allies in the region, according to three people directly familiar with the administration’s internal legal argument.

The legal analysis rests on a premise – for which there is no immediate public evidence – that the cartels are waging armed violence against the security forces of allies like Mexico, and that the violence is financed by cocaine shipments.

As a result, according to the legal analysis, the strikes are targeting the cocaine, and the deaths of anyone on board should be treated as an enemy casualty or collateral damage if any civilians are killed, rather than murder.

That line of reasoning, which forms the backbone of a classified justice department office of legal counsel (OLC) opinion, provides the clearest explanation to date how the US satisfied the conditions to use lethal force.

But it marks a sharp departure from Donald Trump’s narrative to the public every time he has discussed the 21 strikes that have killed more than 80 people, which he has portrayed as an effort to stop overdose deaths.

A White House official responded that Trump has not been making a legal argument. Still, Trump’s remarks remain the only public reason for why the US is firing missiles – when the legal justification is in fact very different.

And it would also be the first time the US has claimed – dubiously, and contrary to the widely held understanding – that the cartels are using cocaine proceeds to wage wars, rather than to make money.

In a statement, a justice department spokesperson said: “These operations were ordered consistent with the law of armed conflict.” The Pentagon did not respond to a request for comment.

The new rationale being advanced by the administration comes as the legal justification gains heightened importance amid a military campaign against the cartels that shows signs of dramatically expanding.