The United Kingdom is no longer sharing intelligence with the US about suspected drug trafficking vessels in the Caribbean because it does not want to be complicit in US military strikes and believes the attacks are illegal, sources familiar with the matter told CNN.

The UK’s decision marks a significant break from its closest ally and intelligence sharing partner and underscores the growing skepticism over the legality of the US military’s campaign around Latin America.

For years, the UK, which controls a number of territories in the Caribbean where it bases intelligence assets, has helped the US locate vessels suspected of carrying drugs so that the US Coast Guard could interdict them, the sources said. That meant the ships would be stopped, boarded, its crew detained, and drugs seized.

The intelligence was typically sent to Joint Interagency Task Force South, a task force stationed in Florida that includes representatives from a number of partner nations and works to reduce the illicit drug trade.

But shortly after the US began launching lethal strikes against the boats in September, however, the UK grew concerned that the US might use intelligence provided by the British to select targets. British officials believe the US military strikes, which have killed 76 people, violate international law, the sources said. The intelligence pause began over a month ago, they said.