Senior US national security officials said on Wednesday that military operations against cartels would continue, setting the stage for a sustained military campaign in Latin America even as basic questions about a deadly strike against a vessel from Venezuela remained unanswered.

The US military killed 11 people on Tuesday in a strike on a vessel from Venezuela allegedly carrying illegal narcotics, in the first known operation since President Donald Trump's recent deployment of warships to the southern Caribbean.

Little is known about the strike, including what legal justification was used or what drugs were on board, but US Defense Secretary Pete Hegseth said operations would continue.

"We've got assets in the air, assets in the water, assets on ships, because this is a deadly serious mission for us, and it won't stop with just this strike," Hegseth said on Fox & Friends.

"Anyone else trafficking in those waters who we know is a designated narco terrorist will face the same fate," Hegseth said.

He declined to provide details on how the operation was carried out, saying they were classified. It is unknown whether the vessel was destroyed using a drone, torpedo, or by some other means.

Secretary of State Marco Rubio, speaking in Mexico City, said similar strikes will happen again.

"Maybe it's happening right now, I don't know, but the point is the president of the United States is going to wage war on narco terrorist organisations," Rubio said.

Trump said on Tuesday, without providing evidence, that the US military had identified the crew of the vessel as members of Venezuelan gang Tren de Aragua, which Washington designated a terrorist group in February.

On Wednesday, he told reporters in the Oval Office that "massive amounts of drugs" were found on the boat.

"We have tapes of them speaking," said Trump. "It was massive amounts of drugs coming into our country to kill a lot of people. And everybody fully understands that. In fact you see it, you see the bags of drugs all over the boat," Trump said.

The Pentagon has not released specifics about the crew nor why it chose to kill those on board.

Presidents of both major US parties have in the past asserted the authority to use the military for limited strikes when there is a threat to the United States, as Trump did in June when he ordered an attack on Iran.

Rubio said that "a boat full of cocaine or fentanyl" was an immediate threat to the United States, adding that Trump had the right to "eliminate (it) under exigent circumstances."

Mary Ellen O'Connell, an expert on international law and the use of force at the University of Notre Dame, said Tuesday's operation "violated fundamental principles of international law."

"The alleged fact that the attack was on the high seas is irrelevant. What is relevant is that the US had no right to intentionally kill these suspects," she said. (Reuters)