Three men have been killed in a US strike on an alleged drug-smuggling boat in the Caribbean, US Defence Secretary Pete Hegseth has said.

It is the latest in a series of attacks on vessels the Trump administration says are being used to smuggle drugs into the US.

Since they began in September, experts have questioned the legality of the strikes under international law, which have drawn strong criticism from Latin American leaders whose citizens have been targeted.

Combatting the flow of illegal drugs is a key policy for US President Donald Trump - but some have suggested the strikes are part of efforts to influence politically opposed governments in the region.

Hegseth said the boat targeted on Saturday was operated by a designated terrorist organisation - without specifying which one - and had been travelling in international waters when it was hit.

The vessel was reportedly travelling along a known drug-smuggling route and carrying narcotics, he said, without providing evidence.

His statement late on Saturday was accompanied by a video that appears to show a blurred-out boat travelling through the water before exploding.

Announcements of these strikes are typically accompanied with grainy footage but lack evidence of the alleged drug trafficking and few details about who or what was on board each vessel.

The Trump administration has claimed that some boats targeted had departed from Venezuela.

According to CBS News, at least 64 people have been killed by American airstrikes in the Caribbean and eastern Pacific since early September.

Colombian President Gustavo Petro has previously labeled the attacks as murder and claimed they are being used by the US to dominate Latin America. Venezuela's Nicolas Maduro accused Washington of fabricating a war.

Following Petro's criticisms, the US placed sanctions on him and his government officials, while also revoking Colombia's certification as an ally in the war on drugs.

Trump has hinted at military action against land targets in Venezuela but admits this may require the consent of the US Congress.

However, some US lawmakers have asserted that the strikes on vessels also required congressional approval - something Trump has denied.

The UN's human rights chief Volker Turk stated that the attacks violate international human rights law, saying these acts find no justification under such laws.

Military analysts argue that the US's buildup of warships and military assets in the Caribbean far exceeds what would be necessary for drug enforcement operations, raising concerns about the true intentions behind these operations.