Washington DC - Senator Mark Kelly said on Sunday that the Armed Services Committee will investigate the Trump administration's reported follow-up strikes on a boat in the Caribbean, as Senator Chris Van Hollen warned of possible war crimes.

"I think there needs to be an investigation," Kelly said when asked by Kristen Welker on NBC's Meet the Press whether such strikes constitute illegal orders.

"We're going to have an investigation," the Arizona Democrat, who sits on the Senate Armed Services Committee, continued. "We're going to have a public hearing. We're going to put these folks under oath. And we're going to find out what happened. And then, there needs to be accountability."

Kelly's statement came amid reports that US forces conducted a follow-up attack on a boat off the coast of Venezuela on September 2.

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In that incident, the US military saw two survivors of an initial strike clinging to the burning vessel, and proceeded to strike the boat again, according to The Washington Post.

Prior to the operation, the troops had been given a directive from Defense Secretary Pete Hegseth to kill everyone on board, The Washington Post and CNN both reported, citing unnamed sources familiar with the operation.

The Trump administration has threatened to court-martial Kelly, a former Navy combat pilot, over a video he shared along with other Democrats urging US troops to refuse illegal orders.

When asked whether he would refuse to carry out the boat attacks if he were still in uniform, the former astronaut did not give a straight "yes" or "no" answer but did note there was a difference between the initial strike and the reported second strike.

The Trump administration has claimed – without providing evidence – that its boat strikes in the Caribbean and eastern Pacific are targeting alleged drug traffickers. The attacks have killed at least 83 people.

UN Human Rights chief Volker Turk has urged Washington to investigate the strikes' legality, saying there was "strong evidence" they constitute extrajudicial killings.

Senator Chris Van Hollen on Sunday warned it's "very possible" that the reported September 2 follow-up strike constitutes a war crime.

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"Of course, for it to be a war crime, you have to accept the Trump administration's whole construct here, which is we're in armed conflict, at war, with this particular – with the drug gangs," Van Hollen said on ABC's This Week.

"Of course, they've never presented the public with the information they've got here. But it could be worse than that, right? If that theory is wrong, then it's plain murder," the Maryland Democrat explained.

"I'm saying that it's either murder from the first strike, if their whole theory is wrong – and I think, you know, the weight of the legal opinion here is that they have concocted this ridiculous legal theory," the senator said. "But even if you accept their legal theory, then it is a war crime."

"And so I do believe that the secretary of defense should be held accountable for giving those kind of orders."

Trump has defended Hegseth's actions, telling reporters aboard Air Force One on Sunday: "I'm going to find out about it, but Pete said he did not order the death of those two men."

When asked if he would have wanted a second attempt to kill the survivors, Trump said: "We'll look into it, but no, I wouldn't have wanted that – not a second strike. The first strike was very lethal."

Hegseth has dismissed the reports as "fake news."

Late Sunday, the defense secretary posted a mockup cover of a book featuring the children's character Franklin the Turtle, entitled "Franklin Targets Narco Terrorists."

The turtle, wearing a US military vest, is shooting from a helicopter at boats crewed with armed men. "For your Christmas wish list," Hegseth wrote on his personal account on X.