Australian Prime Minister Scott Morrison is calling the deaths of three American firefighters in New South Wales “a terrible tragedy.”

The three, who were in Australia helping fight that country’s ongoing wildfires, were in a C-130 Hercules firefighting aircraft carrying a load of retardant when the plane went down in New South Wales, according to news reports. Authorities said wreckage and the crash site have been located – but no survivors.

The identities of the victims have not yet been released.

“My deepest condolences to the loved ones, friends and colleagues of those who have lost their lives,” tweeted Morrison.

The aircraft was operated by Coulson Aviation, an American company contracted by the Rural Fire Service. Following the crash, Coulson Aviation grounded its large air tankers as a precaution. The company has been active in firefighting in New South Wales for years.

The Australian Transport Safety Bureau will be investigating the crash.

Dozens of blazes continue to burn out of control in New South Wales and other areas. More than 200 U.S. Forest Service and Department of Interior personnel are assisting Australia with responding to the wildfires.