​Four people have been killed after the United States military struck a vessel in the Caribbean Sea that it alleged was being used to traffic illegal drugs.

The US Southern Command said the operation was conducted on Saturday along a known smuggling route. However, officials did not disclose the vessel’s precise location, destination or the identities and nationalities of those killed.

No evidence was publicly released confirming that narcotics were aboard the vessel.

Footage published by Southern Command reportedly showed a boat travelling across the water before a sudden flash appeared. There were no reported survivors.

The strike is the latest in an expanding US military campaign targeting vessels suspected of transporting drugs through the Caribbean Sea and eastern Pacific Ocean.

At least 231 people have reportedly been killed in 69 strikes since the campaign began nearly a year ago. US authorities have generally described those targeted as drug traffickers or “narcoterrorists,” although detailed evidence supporting the allegations has rarely been made public.

President Donald Trump’s administration argues that the operations are necessary to disrupt the flow of illegal drugs into the United States and help reduce overdose deaths.

Trump has characterised the campaign as an armed conflict with Latin American drug cartels. That position has raised questions about the legal authority for using lethal military force against suspected traffickers at sea.

The lack of publicly available evidence identifying those aboard the targeted vessels or confirming their alleged cargo has intensified scrutiny of the campaign.

Washington is also expanding its anti-drug operations beyond maritime strikes by seeking closer cooperation with governments across Latin America.

US officials said Colombia, Honduras and Panama have agreed to various forms of joint military cooperation against criminal organisations. Guatemala has disputed an American claim that it entered a similar arrangement, while Ecuador began conducting joint missions with the United States earlier this year.