WASHINGTON (AP) — A U.S. Customs and Border Protection agent and a suspected smuggler died during a shootout Thursday off the Puerto Rico coast, authorities said. Two other U.S. officers were injured.

CBP’s Air and Marine Operations unit was on routine patrol when the shots were fired about 12 miles (19 kilometers) off the coast from Cabo Rojo, a major drug smuggling corridor for cocaine coming out of South America known as the Mona Passage. It lies between Puerto Rico’s western coastline and the Dominican Republic.

One of two suspected smugglers died, said CBP spokesman Jeffrey Quiñones.

An internal memo to CBP employees from Troy Miller, the acting Commissioner of Customs and Border Protection, said a Marine Interdiction Agent died Thursday morning.

“At approximately 8 a.m. this morning, three CBP Marine Interdiction Agents were involved in an exchange of gunfire with individuals on board a suspected smuggling vessel,” according to the memo. “The agents suffered various gunshot injuries as a result and were airlifted by CBP and the Coast Guard to the Puerto Rico Trauma Center.”

There was no information on the status of the other two agents.

The FBI is leading the investigation into the shooting, Quiñones told reporters in Puerto Rico. He said it was too early to know where the vessel originated from, the nationality of its two passengers and whether it was carrying narcotics or servicing another suspected drug vessel in the Caribbean.

Typically, drug cartels recruit poor fishermen from Colombia and Venezuela to transport large amounts of cocaine northward to the Dominican Republic where it is broken down into smaller bales and transferred at sea to waiting vessels manned by better-paid, sometimes well-armed Puerto Rican drug runners.

Homeland Security Secretary Alejandro Mayorkas said in testimony before a Senate committee that an Air and Marine Operations agent was killed and several other agents were “gravely wounded.”

“These are brave members of our Air and Marine Operations within U.S. Customs and Border Protection,” Mayorkas said. “So the difficulty of this job cannot be compared to the difficulty that our frontline personnel face every day. Their bravery and selfless service should be recognized.”

Air and Marine Operations employs about 1,650 people and is one of the smaller units of CBP, the largest law enforcement agency in the United States that also includes the Border Patrol. It works to stop the illegal movement of people, drugs and other goods.

The unit detected 218 “conventional aircraft incursions” on U.S. soil in the 2021 fiscal year, seized 1.1 million pounds of narcotics, $73.1 million in illicit currency, made more than 122,000 arrests and recued 518 people, according to CBP.