The classified briefing, led by Defense Secretary Pete Hegseth and Secretary of State Marco Rubio, comes amid mounting unease in Congress over the president's widening campaign in waters off Latin America, and as lawmakers weigh measures to curb Trump's authority to act without their approval.

"I have a lot of questions. What's our end game, and strategy?" Democratic Connecticut Senator Richard Blumenthal told AFP ahead of the briefing.

"Why are we killing people on these boats? What are they carrying? Where are they heading? Who's behind them? And I think the American people -- not just senators -- deserve to hear from both Hegseth and Rubio."

US officials say the operations target narcotics bound for American shores.

Critics counter that the campaign -- which has destroyed at least 26 boats and killed at least 95 people, according to US military figures -- is legally ambiguous and strategically unclear.

The briefing, which will also feature Joint Chiefs Chairman General Dan Caine, precedes a possible Senate vote on resolutions aimed at restricting Trump from launching military action against Venezuela without congressional consent.

Beyond the boat strikes, the administration has ratcheted up pressure on Venezuelan President Nicolas Maduro -- deploying warships and aircraft near his coastline, seizing an oil tanker linked to Caracas, and slapping fresh sanctions on Maduro's family and business allies.

Trump has declared that Maduro's "days are numbered" and pointedly refused to rule out a US ground invasion.

The strikes have drawn particular scrutiny over a September 2 operation in which US forces carried out a second attack on a disabled boat, killing two survivors of the initial strike.

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Senators from both parties say they will demand answers on the legal basis for that attack and why Congress has been denied full access to video footage, which so far has been shown only to a handful of senior lawmakers.

Senate Democratic Minority Leader Chuck Schumer has demanded that the administration provide every senator with the complete, unedited tapes, warning that secrecy -- combined with the presence of US troops and a carrier group in the region -- risks dragging the country into another open-ended conflict.

Some Republicans, including Senator Rand Paul, have also questioned whether targeting shipwrecked suspects violates international law.

Legal experts say the case highlights a central tension in Trump's approach -- treating drug trafficking as an act of war.

This week, Trump signed an executive order classifying fentanyl as a "weapon of mass destruction," an escalation supporters say reflects the gravity of the opioid crisis.

Specialists note, however, that most of the intercepted boats were believed to be carrying cocaine, not fentanyl.

Despite mounting scrutiny, the campaign shows no sign of slowing.

On Monday, the Pentagon said it had carried out fresh strikes against alleged drug boats in the Pacific, killing eight people described as "narco-terrorists."

The Senate briefing also follows last week's dramatic US seizure of an oil tanker accused of transporting sanctioned Venezuelan fuel in a network linked to Iran.

US officials released video showing armed forces rappelling onto the vessel from a helicopter, an operation Caracas denounced as "international piracy."

Trump's chief of Staff Susie Wiles said in an interview with Vanity Fair the president "wants to keep on blowing boats up until Maduro cries uncle," but acknowledged that Trump would need congressional authorization to carry out strikes in Venezuela that he has recently been saying may come "soon."