AP Photo

Fifty Afghans believed to be drug traffickers with ties to the Taliban have been placed on a Pentagon target list to be captured or killed, reflecting a major shift in American counternarcotics strategy in Afghanistan, according to a Congressional study to be released this week.

United States Marines on a recent raid in Helmand Province. Under a new policy, drug traffickers are subject to being killed.

United States military commanders have told Congress that they are convinced that the policy is legal under the military’s rules of engagement and international law. They also said the move is an essential part of their new plan to disrupt the flow of drug money that is helping finance the Taliban insurgency.

In interviews with the Senate Foreign...