(CNN)Thick fog forced authorities to suspend the air search Wednesday for seven Marines and four Army aircrew, feared dead after their Black Hawk helicopter crashed into waters off the Florida Panhandle.
The helicopter was first reported missing at about 8:30 p.m. (9:30 p.m. ET) Tuesday. Hours later, searchers found debris around Okaloosa Island near Eglin Air Force Base, base spokesman Andy Bourland said.
This debris washed up on both the north and south sides of Santa Rosa Sound, which connects mainland northern Florida and a barrier island.
The air search is expected to resume midday Thursday, the spokesman said. A spokeswoman for the Coast Guard said that boats will continue scouring the waters throughout the night Wednesday, weather permitting.
Human remains have washed ashore in the area near Eglin.
Base spokeswoman Jasmine Porterfield didn't specify what was found, noting the search-and-rescue mission remained underway. Still, there was little hope for a miracle, with Gen. Martin Dempsey -- chairman of the Joint Chiefs of Staff -- expressing his condolences.
He said the crash was "a reminder to us that those who serve put themselves at risk, both in training and in combat."
"We will work with the services to ensure that ... their family members will be well cared for."
The Air Force, Coast Guard and civilian agencies participated in the intensive search focused on where they believe the aircraft went down, in waters east of the town of Navarre and the Navarre Bridge and near Eglin testing range site A-17.
Porterfield said approximately 100 people were involved in canvassing the ground and the waters, looking for debris: "It's a huge effort underway."
No one is saying what caused the accident, with Eglin spokeswoman Sara Vidoni indicating only that there's no indication of anything suspicious.
There was heavy fog in the area when the aircraft went missing, though the Eglin spokeswoman said it's too early to tell whether that had anything to do with the crash.
"There is training in all conditions -- that's part of the military mission," Vidoni said. "They were out there doing what the military does."
According to Morris, the service members -- all men -- were involved in a seven-day training exercise of amphibious operations. It involved small boats and inserting and extracting Marines from the water via helicopter. Morris would not say in which phase of the training the Marines were on Tuesday night.
The UH-60 helicopter wasn't alone when it went down. A second Black Hawk -- assigned to 1-244th Assault Helicopter Battalion based in Hammond, Louisiana -- safely returned to the base, some 40 miles east of Pensacola.
The aircraft were both assigned to the Louisiana Army National Guard out of Hammond and taking part in what the U.S. military called a "routine training mission involving the Marine Special Operations Regiment" out of Camp Lejeune.
"Whatever the trouble was with the one aircraft, it did not involve the second helicopter that was participating in the exercise," Bourland said.
