The United Kingdom has ceased sharing intelligence with the United States regarding suspected drug trafficking vessels in the Caribbean, according to sources familiar with the situation who spoke with CNN. The decision stems from the UK’s reluctance to be associated with US military actions, which it views as illegal.

This move signifies a notable shift in the UK’s collaboration with its closest ally and intelligence-sharing partner, highlighting increasing doubts about the legality of the US military operations in Latin America.

Historically, the UK has played a crucial role in assisting the US by locating vessels suspected of drug trafficking. The UK, which maintains several territories in the Caribbean equipped with intelligence assets, has traditionally supported US efforts to intercept these vessels. This involved the US Coast Guard stopping, boarding, detaining crews, and confiscating drugs, according to sources.

Typically, such intelligence was relayed to the Joint Interagency Task Force South, a Florida-based task force comprising representatives from various partner nations, dedicated to curbing the illicit drug trade.

However, the dynamic changed in September when the US began conducting lethal operations against these boats. The UK grew increasingly concerned that its intelligence might be used by the US to identify targets. British officials believe these military strikes, which have resulted in 76 fatalities, breach international law, prompting them to halt intelligence sharing over a month ago, sources revealed.

The UN’s human rights chief, Volker Türk, said last month that the strikes violate international law and amount to “extrajudicial killing.” The UK agrees with that assessment, the sources told CNN.

The British embassy in Washington and the White House did not respond to requests for comment. A Pentagon official told CNN that the department “doesn’t talk about intelligence matters.”

Before the US military began blowing up boats in September, countering illicit drug trafficking was handled by law enforcement and the US Coast Guard, Cartel members and drug smugglers were treated as criminals with due process rights – something the UK was happy to help with, the sources said.

But the Trump administration has argued that the US military can legally kill suspected traffickers because they pose an imminent threat to Americans and are “enemy combatants” who are in an “armed conflict” with the US, according to a memo sent by the administration to Congress.

The Justice Department’s Office of Legal Counsel issued an opinion, which is still classified, reinforcing that argument, CNN has reported, and Trump has designated a number of drug cartels as “foreign terrorist groups.” The White House has said repeatedly that the administration’s actions “comply fully with the Law of Armed Conflict,” the area of international law that is designed to prevent attacks on civilians.

But legal experts say the Law of Armed Conflict would still apply to civilian drug traffickers, and the designation of a group as a foreign terrorist organisation does not automatically authorise the use of lethal force.

Several boats hit by the US have either been stationary or were turning around when they were attacked, CNN has reported, undermining the administration’s claim that they posed an imminent threat that could not be dealt with through interdiction and arrest.

Senior US defence officials have also expressed scepticism of the military campaign. The commander of US Southern Command, Admiral Alvin Holsey, offered to resign during a tense meeting last month with Secretary of Defense Pete Hegseth and Chairman of the Joint Chiefs of Staff after he raised questions about the legality of the strikes, CNN has reported. Holsey will leave his post in December, just one year into his tenure as the SOUTHCOM chief.

Lawyers specialising in international law within DoD’s Office of General Counsel have also raised concerns about the legality of the strikes, CNN has reported. Multiple current and former uniformed lawyers told CNN that the strikes do not appear lawful. Hegseth’s spokesperson has previously denied that any lawyers involved in the operations have dissented.

Canada, another key US ally which has helped the US Coast Guard interdict suspected drug traffickers in the Caribbean for nearly two decades, has also distanced itself from the US military strikes.

The sources told CNN that Canada intends to continue its partnership with the Coast Guard, called Operation Caribbean. But the country has made clear to the US that it does not want its intelligence being used to help target boats for deadly strikes, the sources told CNN.