WASHINGTON (AP) — The Trump administration has yet to provide underlying evidence to lawmakers proving that alleged drug-smuggling boats targeted by the U.S. military in a series of fatal strikes were in fact carrying narcotics, according to two U.S. officials familiar with the matter.

As bipartisan frustration with the strikes mounts, the Senate was voting Wednesday on a war powers resolution that would require the president to seek authorization from Congress before further military strikes on the cartels.

The military has carried out at least four strikes on boats that the White House said were carrying drugs, including three it said originated from Venezuela. It said 21 people were killed in the strikes.

The officials, who were not authorized to comment publicly about the matter and spoke on the condition of anonymity, said the administration has only pointed to unclassified video clips of the strikes posted on social media by President Donald Trump and Defense Secretary Pete Hegseth and has yet to produce “hard evidence” that the vessels were carrying drugs.

The administration has not explained why it has blown up vessels in some cases, while carrying out the typical practice of stopping boats and seizing drugs at other times, one of the officials said.

The Republican administration in a retroactive memo justifying one of the strikes last month declared drug cartels to be “unlawful combatants” and said the United States is now in an “armed conflict” with them.

The declaration has raised stark questions about how Trump intends to use his war powers. It also has been perceived by several senators as pursuing a new legal framework to carry out lethal action and has raised questions about the role of Congress in authorizing any such action.

Asked about the lack of underlying evidence provided to Congress, the Pentagon on Wednesday pointed to videos of the strikes, which do not confirm the presence of drugs.

The Pentagon also noted public statements by Hegseth, including a social media post following the latest fatal strike in which he said, “Our intelligence, without a doubt, confirmed that this vessel was trafficking narcotics, the people onboard were narco-terrorists, and they were operating on a known narco-trafficking transit route.”

Lawmakers have expressed frustration that the administration is offering little detail about how it came to decide the U.S. is in armed conflict with cartels or even detailing which criminal organizations it claims as “unlawful combatants.”

Trump administration officials have argued that the strikes are necessary acts of self-defense as cartels funnel drugs into the United States that they say are leading to thousands of U.S. deaths. While Venezuela produces cocaine, the bulk of it is sent to Europe.