The White House said a Navy admiral acted “within his authority and the law” when he ordered a second, follow-up strike on an alleged drug boat in the Caribbean Sea in a September US military operation that has come under bipartisan scrutiny .

White House press secretary Karoline Leavitt offered the justification on Monday for the September 2 strike as lawmakers announced there would be congressional review of the military strikes against vessels suspected of smuggling drugs in the Caribbean and the eastern Pacific Ocean. The lawmakers cited a published report that Defence Secretary Pete Hegseth issued a verbal order for the second strike that killed survivors on the boat.

Navy Vice Admiral Frank “Mitch” Bradley, who Leavitt said ordered the second strike, is expected to provide a classified briefing on Thursday to lawmakers overseeing the military.

Leavitt did not dispute a Washington Post report that there were survivors after the initial strike. Her explanation came after President Donald Trump a day earlier said he “wouldn’t have wanted that – not a second strike” when asked about the incident.

Late on Monday, Hegseth posted: “Admiral Mitch Bradley is an American hero, a true professional, and has my 100 percent support. I stand by him and the combat decisions he has made – on the September 2 mission and all others since.”

A month after the strike, Bradley was promoted from commander of Joint Special Operations Command to commander of US Special Operations Command.

Concern over the Trump administration's military strikes against the alleged drug-smuggling boats has been building in Congress, but details of this follow-on strike stunned many lawmakers from both parties and generated stark questions about the legality of the attacks and the overall strategy in the region, and particularly towards Venezuelan President Nicolás Maduro.

The lawmakers said they did not know whether last week’s Post report was true, and some Republicans were sceptical. Still, they said the reported attacking of survivors of an initial missile strike posed serious concerns and merited further scrutiny.

The White House weighed in after Trump on Sunday vigorously defended Hegseth. “Pete said he did not order the death of those two men,” he said. He added, “And I believe him.”

Senate Majority Leader John Thune on Monday broadly defended the operations, echoing the Trump administration position that they're necessary to stem the flow of illegal narcotics into the United States.

Senate Democratic leader Chuck Schumer called Hegseth a “national embarrassment” over his response to critics. Schumer demanded that Hegseth release the video of the strike and testify under oath about what happened.

Saying that the ramifications of the report were “serious charges”, Republican senator Roger Wicker of Mississippi, the chairman of the Senate Armed Services Committee, pledged that his panel's investigation would be “done by the numbers. We’ll find out the ground truth”.

Senator Jack Reed, the top Democrat on the committee, who also called for the administration to release the video of the strike, said its inquiry would start “with briefings about what actually happened” from the officials involved. “If they’ve done nothing wrong, then that video should exonerate them completely. Why don’t they release it?” he asked.

The September strike was one in a series carried out by the US military in the Caribbean Sea and eastern Pacific Ocean as Trump has ordered the buildup of a fleet of warships near Venezuela , including the largest US aircraft carrier. More than 80 people have been killed in the strikes. (AP)