(NewsNation) — A U.S. Customs and Border Protection marine agent was killed and others were shot Thursday while exchanging gunfire with a group of people aboard a vessel near the coast of Puerto Rico, officials said.

CBP’s Air and Marine Operations unit was on routine patrol around 8 a.m. Thursday when the shots were fired about 12 miles off the coast from Cabo Rojo, a major drug smuggling corridor for cocaine coming out of South America known as the Mona Passage, the agency said. It lies between Puerto Rico’s western coastline and the Dominican Republic.

Three CBP Marine Interdiction Agents exchanged gunfire with two people who were aboard the suspected smuggling ship, officials said. All three agents were shot and airlifted to local hospitals in Puerto Rico.

One of the agents was later pronounced dead. The extent of the injuries or what condition the agents were in was not clear at the time of their emailed statement to NewsNation.

Officials have not released the identity of the agent who was killed.

It wasn’t immediately clear whether any of the people on board the vessel were injured.

After the shooting, another U.S. marine interdiction crew intercepted another boat nearby, finding firearms and other contraband onboard, Customs and Border Protection said. The two people on that ship were also arrested.

The FBI is leading the investigation into the shooting.

Homeland Security Secretary Alejandro Mayorkas said at a congressional hearing Thursday morning that he was briefed on the “tragic loss of one of our front-line personnel” and said, “Several others were gravely wounded.”

“These are brave members of our air and marine operations within U.S. Customs and Border Protection,” Mayorkas told a Senate panel. “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.