Two FBI agents with the elite Hostage Rescue Team were killed Friday during a training exercise off the coast of Virginia Beach, Va. Special Agents Christopher Lorek, 41, and Stephen Shaw, 40, were the victims, the FBI said in a statement Sunday. The FBI did not disclose their cause of death, but reported a helicopter was involved in the incident. 

“We mourn the loss of two brave and courageous men,” FBI Director Robert S. Mueller said in the statement. “Like all who serve on the Hostage Rescue Team, they accept the highest risk each and every day, when training and on operational missions, to keep our nation safe. Our hearts are with their wives, children and other loved ones who feel their loss most deeply. And they will always be part of the FBI family.”

WAVY-TV in Portsmouth, Va., reported the accident occurred while the agents were aboard a Military Sealift Command ship borrowed by the FBI from the Navy. No Navy personnel were injured. The two agents were rushed by helicopter to Sentara Norfolk General Hospital in Norfolk, Va.

A representative of the Norfolk Medical Examiner’s office told WAVY that the two FBI agents’ cause of death will not be revealed until at least Monday.

Lorek joined the FBI in 1996 and is survived by his wife and two daughters. Shaw joined the FBI in 2005 and is survived by his wife, daughter and son. 

The FBI’s Hostage Rescue Team was formed in 1982 as an elite outfit capable of rescuing American hostages held by well-trained and well-armed criminal groups. The Hostage Rescue Team was first deployed as a security measure during the 1984 Los Angeles Olympic Games.