The latest attacks were reportedly carried out in international waters on Sunday and on the direct orders of President Donald Trump.
"These vessels were known to our intelligence service, they had a connection to illegal drug smuggling and were transporting drugs," Hegseth writes on X, referring to the crews as "narco-terrorists."
Tensions between the United States and Latin American countries such as Colombia and Venezuela have escalated since the United States carried out several attacks on ships allegedly transporting drugs off the countries' respective coasts.
Around 70 people have been killed in the attacks that have taken place in both the Pacific and Caribbean Seas.
UN human rights chief Volker Türk tells the AFP news agency that the US must look more closely at whether the attacks are extrajudicial.
"I have called on the US government in particular to investigate (the attacks), because they have to ask themselves whether this is a violation of international human rights law. Is this an extrajudicial killing? I mean, there is strong evidence that it is, but they have to investigate this," he said.
