US President Donald Trump signed an executive order Monday designating illicit fentanyl as a "weapon of mass destruction".
"We're formally classifying fentanyl as a weapon of mass destruction, which is what it is," Trump said. "No bomb does what this is doing."
The decision came as US military confirmed a new strike on three vessels accused of drug trafficking in the eastern Pacific Ocean on Monday, killing eight people.
US Southern Command said the strikes targeted "designated terrorist organisations", killing three people on the first boat, two on the second and three on the third.
The military released a video showing a boat moving through water before exploding.
Trump has justified the attacks as necessary to stem drug flows into the US and has declared the country is in an "armed conflict" with drug cartels.
The Trump administration faces mounting pressure from lawmakers over the strikes, which have killed at least 95 people in 25 attacks since early September. One attack killed two survivors clinging to wreckage after an initial strike.
The latest attacks came ahead of scheduled classified briefings on Capitol Hill. US Defence Secretary Pete Hegseth and Secretary of State Marco Rubio briefed congressional leaders on Tuesday but lawmakers said they remained unsatisfied with the administration's explanations.
Senate Democratic leader Chuck Schumer called the briefing "very unsatisfying" and said Hegseth refused to commit to releasing full video of the September double-strike incident. Asked whether he would allow Congress to view unedited footage, Hegseth responded: "We have to study it," according to Schumer.
Congress has included provisions in its annual defence bill demanding the Pentagon turn over unedited strike videos and threatening to withhold a quarter of Hegseth's travel budget if he refuses.
The campaign has increased pressure on Venezuelan President Nicolás Maduro, whom the US accuses of narco-terrorism. US forces last week seized a sanctioned oil tanker that Washington says smuggled illicit crude.
The US government does not recognise Maduro's legitimacy and accuses him of leading the Cartel of the Suns, an alleged drug trafficking group linked to Venezuela's government, which officials in Caracas dismiss as an invention.
Trump has said ground attacks will begin soon, though he has not given details. The US has deployed its largest military presence in the region in decades.
Maduro responded by saying he was confident Americans would "tie the hands" of those seeking war.
"I know that the people of the United States are going to tie the hands of the war-mongering madmen who want to impose a war for oil in South America," he said in his weekly programme Con Maduro+ broadcast on Venezuelan television Monday.
