The U.S. military launched a strike on another boat accused of carrying drugs in the eastern Pacific Ocean on Tuesday, killing four people in the fourth such attack announced in the past few days.

U.S. Southern Command posted aerial video on social media Tuesday showing a vessel bobbing in the water before being struck by a projectile and exploding. The military earlier said it struck two boats on Saturday and a third on Monday.

The military said all the vessels were “operated by Designated Terrorist Organizations” and that intelligence confirmed they “were transiting along known narco-trafficking routes in the Eastern Pacific and were engaged in narco-trafficking operations” but did not provide evidence.

Asked about another strike in the eastern Pacific that killed two men on Monday, a spokesperson for U.S. Southern Command told CBS News: “For operational security reasons, we cannot discuss specific sources or methods.”

The latest strike brings the death toll to 175 since the operations began in early September. The U.S. Coast Guard has suspended the search for one survivor from an attack Saturday.

In at least six instances, people have survived the strikes on alleged drug trafficking boats, spurring efforts to find and rescue them in most cases. Authorities have later called off several of those searches, though in one October operation, two survivors were picked up by a Navy helicopter and repatriated to their home countries of Ecuador and Colombia.

During the first boat strike in the Trumo administration’s controversial campaign on Sept. 2, two people survived an initial strike but were killed in a follow-on attack, prompting accusations the second strike may have constituted a war crime.

Critics have questioned the overall legality of the boat strikes as well as their effectiveness, in part because the fentanyl behind many fatal overdoses is typically trafficked to the U.S. over land from Mexico, where it is produced with chemicals imported from China and India.

President Trump has said the U.S. is in “armed conflict” with cartels in Latin America and has justified the attacks as a necessary escalation to stem the flow of drugs into the United States and fatal overdoses claiming American lives. But his administration has offered little evidence to support its claims of killing “narcoterrorists.”