The attack, in the eastern Pacific, was part of a continuing campaign by the U.S. Southern Command to target people suspected of smuggling drugs by sea.

Legal specialists on the use of lethal force have said the strikes are illegal, extrajudicial killings.

© US Southern Command, via Reuters

It was the first time in the campaign against people the United States accuses of drug smuggling at sea that American forces blew up boats on both sides of the Panama Canal in the same day.

© Eric Lee for The New York Times

The strike in the eastern Pacific, the third on suspected drug trafficking boats this year, was the second authorized by Gen. Francis L. Donovan, the new head of the Southern Command.

© Tom Brenner/Getty Images

Lt. Gen. Francis L. Donovan, a Marine general with expansive experience in special operations and the Middle East, would take over after the abrupt departure of the previous commander.

© U.S. Marine Corps