Two members of the FBI's Hostage Rescue Team (HRT) died Friday during a training exercise off the coast of Virginia Beach, the agency announced.

Special agents Christopher Lorek, 41, and Stephen Shaw, 40, had served the FBI for 17 years and eight years respectively. The HRT is part of the FBI's Critical Response Group and is based in Quantico, Va.

"We mourn the loss of two brave and courageous men," FBI Director Robert Mueller said in a 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."

The agents were using a ship the FBI had leased from the Navy's Military Sealift Command during the training. The medical examiner's office said Monday it could be months before he can determine cause of death, reports the Virginian-Pilot.

Lorek leaves behind a wife and two daughters. Shaw leaves behind a wife, daughter, and son.