Human remains washed ashore Wednesday, as officials continued their search for seven Marines and four soldiers in waters off the Florida Panhandle, where a military helicopter had crashed during a training exercise.

“We have confirmed that we have had some human remains wash ashore in the area where our search and rescue team have begun a larger scale operation,” Andrew Bourland, a spokesman for the Eglin Air Force Base, told The Washington Post.

The Army UH-60 Black Hawk is believed to have gone down in the water and foggy conditions were reported in the area at the time of the crash, though it is too soon to say what might have caused the mishap.

At a Wednesday afternoon news conference, Maj. Gen. Glenn H. Curtis, the Adjutant General for the Louisiana National Guard, said the Black Hawk pilots had thousands of hours of flight experience and were “instructor pilots,” which indicates that they were experienced and qualified enough to train other pilots.

According to Curtis, it is one of the highest designations pilots in the Army can receive.

A second Black Hawk that participated in the exercise returned to base after take-off due to the weather conditions, Curtis said.  That helicopter landed safely and all personnel on board were accounted for.

“One of them started to take off and realized that the weather was a condition then turned around and came back,” said Curtis, who spoke from Hammond, La.

According to a Pentagon official who spoke anonymously to the Associated Press nearly 12 hours after the craft was reported missing, all 11 service members are presumed dead.

Foggy conditions in the search area have made the operation more difficult, Bourland told The Post. But with the break of dawn, efforts ramped up.

“We’ve got some daylight, but it is overcast and quite foggy,” Bourland said earlier on Wednesday. “It is having an impact on getting the full-scale rescue moving now.”

Local authorities, the Florida Fish and Wildlife Conservation Commission, and the Coast Guard were involved in the search efforts, according to a news release.

The helicopter carrying highly trained Marines in a special operations unit, was on a night training mission outside the base, which is near Valparaiso, Fla. Crews were dispatched after the Eighth Coast Guard District Command Center got a report of a downed military aircraft late Tuesday evening, the release stated. A “debris field consistent with a military aircraft” was located at around 1:30 a.m. CST on Wednesday, according to the Coast Guard release.

The helicopter does contain a flight data recorder, the Army said on Wednesday, that can be recovered as investigators try to determine what caused the accident.

“Our thoughts and prayers are with the friends and family of the members involved in this incident,” Layne Carter, search and rescue mission coordinator, said in the release. “We are aggressively searching for possible survivors involved in the crash.”

The Marines are part of a Camp Lejeune-based special operations group and the soldiers are from an Army National Guard unit based out of Hammond, La.

“Our thoughts and prayers are with the Marines, soldiers and family members of those involved in this mishap. We are working closely with all parties involved to locate our Marines and the Army aircrew as soon as possible,” Maj. Gen. Joseph Osterman, commander of U.S. Marine Corps Forces, Special Operations Command said in a statement.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, on Wednesday told members of the Senate Foreign Relations Committee that the crash reinforces the fact that military personnel are “at risk whether in training or in combat.”

“Our thoughts and prayers with them,” Defense Secretary Ashton B. Carter said, while speaking on Capitol Hill.

The names of the aircrew and Marines are being withheld while the search and rescue mission is ongoing.

“Today, as you can imagine, is a tough day for the Louisiana National Guard and the Marine Corps,” Curtis said. “At this hour, our priorities are search and rescue for our soldiers and Marines. And secondly to take care of our families. This will remain a search and rescue operation.”

 [This post has been updated multiple times.]