Four US Army soldiers are presumed dead after an MH-60 Black Hawk helicopter crashed Wednesday night near Summit Lake and Joint Base Lewis-McChord, officials said Friday.

The aircraft — assigned to the 160th Special Operations Aviation Regiment — was on a routine training flight when it went down around 9 PM Recovery operations are underway and the cause is under investigation. The Army said the soldiers’ names are being withheld pending notification of families and that additional information is expected Monday.

Access to the crash site has been difficult because of dense forest and the location, authorities said.

“It’s very rural and it was hard to get to and we don’t know what happened,” Lt. Col. Allie Scott, an Army spokesperson, said Thursday.

The Thurston County Sheriff’s Office said deputies located the wreckage, but efforts were hampered by a brush fire at the scene; “the scene is on fire,” Sheriff Derek Sanders noted on social media.

Local agencies, including the Lacey Police Department, assisted with a drone to assess the area. The helicopter and crew were based at the joint base.