The US military said it killed four more people in a boat strike in the eastern Pacific ocean on Tuesday, marking the third deadly attack on vessels in the region in four days.

The US Southern Command, which oversees military operations in Latin America and the Caribbean, announced the killings in a social media post, claiming, without providing evidence, that the men killed were “narco-terrorists”.

The US military’s boat strikes have now killed at least 174 people since September.

Military officials have consistently alleged that the targets of its lethal boat strikes were “engaged in narco-trafficking operations” but have not presented intelligence or specific details about the individuals to support those assertions.

Legal experts and human rights advocates have repeatedly condemned the strikes as extrajudicial killings that violate US and international law, saying the military cannot execute civilians whom it accuses of crimes.

The US Southern Command’s post on Tuesday included another blurry aerial video showing a boat exploding, with a statement alleging that “intelligence confirmed the vessel was transiting along known narco-trafficking routes”.

The announcement used nearly identical language as the military’s alert on Monday, which said it had killed two people in a boat strike. On Sunday, the US Southern Command said it had killed five people in vessel explosions, and that there was one survivor.

Donald Trump has sought to justify the attacks by claiming the US is engaged in an “armed conflict” with Latin American cartels. But United Nations officials have said international humanitarian law does not allow the US to kill people accused of drug trafficking and noting the military has not provided evidence that the people on the targeted boats posed an imminent threat to the lives of others.

In January, lawyers filed a federal lawsuit against the US on behalf of the families of two men from a fishing village in Trinidad who were killed in an October strike on a small boat in the Caribbean, saying the “premeditated and intentional killings lack any plausible legal justification”.

“The administration continues to push unsubstantiated, fear-mongering claims about who these people were, despite investigations showing that some of those killed were fishermen just trying to make a living for their families,” the American Civil Liberties Union said in December.

The president was trying to set a precedent that it can redefine civilians as “combatants” and “pretend he has the authority to grant advance immunity to federal officials for killing people”, the ACLU wrote.

Last month, the Democratic representatives Joaquin Castro and Sara Jacobs wrote to the Inter-American Commission on Human Rights, raising alarms about the killings and noting the names and nationalities of most victims remain unknown.

“Each killing took place outside of any recognized armed conflict and without due process. We agree with the overwhelming consensus of legal experts: the administration has engaged in a prolonged campaign of extrajudicial killings, or, in simple terms, murders,” the Congress members wrote.