US officials say they have carried out a number of strikes on boats in the Caribbean Sea, killing multiple drug traffickers.

Announcing the first of these in September, President Donald Trump said his forces had destroyed a vessel that had departed from Venezuela. He said the boat was operated by the Tren de Aragua cartel and was carrying drugs bound for the US.

Similar announcements have followed in recent weeks, accompanied with grainy footage.

Trump’s officials say they are acting in self-defence by destroying boats carrying illicit drugs to the US. But they have not provided evidence of the alleged drug trafficking or details about who or what was on board each ship, and the strikes have attracted condemnation in the region.

In one case, the Colombian president said a boat hit by the US was not Venezuelan, but “Colombian with Colombian citizens inside” – which the White House denied.

After the first of these strikes, BBC Verify spoke to a range of experts in international and maritime law, with several saying that US may have acted illegally in attacking the vessel.

The US is not a signatory to United Nations Convention on the Law of the Sea, but the US military’s legal advisors have previously said that the US should “act in a manner consistent with its provisions”.

Under the convention, countries agree not to interfere with vessels operating in international waters. There are limited exceptions to this which allow a state to seize a ship, such as a “hot pursuit” where a vessel is chased from a country’s waters into the high seas.

“Force can be used to stop a boat but generally this should be non-lethal measures,” Prof Luke Moffett of Queens University Belfast said.

Prof Moffett added that the use of aggressive tactics must be “reasonable and necessary in self-defence where there is immediate threat of serious injury or loss of life to enforcement officials”, noting that the US moves were likely “unlawful under the law of the sea”.

Experts have also questioned whether the killing of the alleged members of the Tren de Aragua cartel could contravene international law on the use of force.

Under Article 2(4) of the UN charter, countries can resort to force when under attack and deploying their military in self-defence. Trump has previously accused the Tren de Aragua cartel of conducting irregular warfare against the US, and the state department has designated the group as a Foreign Terrorist Organisation.

After the first strike, Prof Michael Becker of Trinity College Dublin told BBC Verify that the American action “stretches the meaning of the term beyond its breaking point”.

“The fact that US officials describe the individuals killed by the US strike as narco-terrorists does not transform them into lawful military targets,” Prof Becker said. “The US is not engaged in an armed conflict with Venezuela or the Tren de Aragua criminal organisation.”

Prof Moffett added: “Labelling everyone a terrorist does not make them a lawful target and enables states to side-step international law.”

A memo sent to the US Congress, which was leaked, reportedly said the Trump administration had determined the US was in a “non-international armed conflict” with drug cartels.

Responding to a fifth strike in October, Dame Law School Prof Mary Ellen O’Connell told BBC Verify that “no credible facts or legal principles have come to light to justify these attacks”.

“The only relevant law for peace is international law – that is the law of treaties, human rights and statehood,” Prof O’Connell wrote in an emailed statement.

But US officials including Defence Secretary Pete Hegseth have defended the action, which has also been applauded by Republicans in Congress. Republican Senator Lindsey Graham said the first attack was the “ultimate – and most welcome – sign that we have a new sheriff in town”.

Asked about the same strike, a White House official told BBC Verify that Trump had authorised it after the boat left Venezuela crewed by Tren de Aragua members. The official added that the president was committed to using all means to prevent drugs reaching the US.

The Pentagon declined to share the legal advice it obtained before carrying out the strike.

Questions have also been raised as to whether the White House complied with US law in authorising the strike. The US constitution says that only Congress has the power to declare war.

However, Article II – which lays out the president’s powers – says that “the president shall be Commander in Chief of the Army” and some constitutional experts have suggested that this grants the president the power to authorise strikes against military targets. Trump administration sources have previously cited this provision when defending US strikes on Iran.

But it is unclear whether that provision extends to the use of force against non-state actors such as drug cartels.

Rumen Cholakov, an expert in US constitutional law at King’s College London told BBC Verify that since 9/11, US presidents have relied on the 2001 Authorization of Use of Military Force Act (AUMF) when carrying out strikes against groups responsible for the attacks.

“Its scope has been expanded consistently in subsequent administrations,” he added. “It is not immediately obvious that drug cartels such as Tren de Aragua would be within the President’s AUMF powers, but that might be what ‘narco-terrorists’ is hinting at.”

Questions also remain as to whether Trump complied with the War Powers Resolution, which demands that the president “in every possible instance shall consult with Congress before introducing United States Armed Forces into hostilities”.

Despite some Republicans in Congress reportedly having anxieties about the strikes, the Senate defeated a resolution in October that would have required the Trump administration to seek the approval of Congress before any further attacks.

Venezuela’s government has reacted to the strikes with anger. Its president, Nicolas Maduro, denies American accusations that he is involved with drugs trafficking.

The strikes come amid reports that the US has deployed several naval warships to the region in support of anti-narcotics operations against Venezuela.

BBC Verify has not been able to track all of these vessels. But using information from publicly available onboard trackers, and videos on social media, we’ve potentially identified four of them in the region.

A ship identifying itself as the USS Lake Erie – a guided missile cruiser – last transmitted its location in the Caribbean Sea on 30 August, east of the Panama Canal.

Two others identifying themselves as the USS Gravely and USS Jason Dunham last transmitted their locations in mid-August, at the American base in Guantanamo Bay. A fourth, the USS Fort Lauderdale, transmitted its location north of the Dominican Republic on 28 August.

Trump – who has long sought to oust Maduro – has authorised a US$50m reward for any information leading to his arrest. The Venezuelan leader claimed victory in last year’s elections, widely viewed as rigged by international observers.

Additional reporting by Lucy Gilder