Two FBI special agents were killed during a training exercise off the coast of Virginia Beach, Virginia. They were part of the agency's elite counterterrorism unit, the Hostage Rescue Team, based in Northern Virginia.

No other details were given about the deaths of the special agents. The FBI said in a statement that the cause of the incident was "under review."

The agents were identified as Christopher Lorek, 41, and Stephen Shaw, 40. They were in the FBI's Hostage Rescue Team, which is part of the Critical Incident Response Group.

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

Lorek joined the FBI in 1996 and has a wife and two daughters, 11 and 8. Shaw joined in 2005 and is survived by his wife, daughter and son, 3 and 1 respectively.

An FBI spokeswoman in the Virginia Beach area said the deaths did not involve gunfire, The Washington Post reported.

According to AP, the Hostage Rescue Team was formed 30 years ago in preparation for the 1984 Olympics hosted in Los Angeles. Members are trained in military tactics and wield combat-style weapons. They provide quick assistance to local FBI offices during hostage situations and have been involved in hostage situations more than 800 times since 1983.