A helicopter involved in efforts to battle a wildfire in California’s Yosemite National Park crashed, killing the two pilots on board, according to fire officials.

The crash occurred Sunday afternoon during firefighting operations, according to the Federal Aviation Administration. Two people were on board the Eurocopter AS32 helicopter, the agency said.

The helicopter was performing a water bucket operation and actively dropping water on the fire when it crashed southeast of Lake Ostrander in Yosemite, according to Benjamin Cossel, spokesperson for California Complex Incident Management Team 3, which is overseeing the Dome Fire response.

The remains of the pilots were successfully recovered Monday afternoon, Cossel told ABC News.

“This is extremely challenging on everybody here,” Cossel said. “The wildland firefighting world is an extremely small community. We all know each other, and if we don’t know each other, it’s just because we haven’t met each other yet. So this is devastating to the wildland firefighting community, and we’re all doing our best to get through it right now.”

The private helicopter was owned by contractor Precision, according to Cossel.

“It is with unimaginable sadness and broken hearts that we share the loss of two beloved members of our team,” Precision said in a statement on social media on Sunday. “We are devastated by this loss and are struggling to find the words.”

The Alaska Division of Forestry & Fire Protection identified one of the deceased pilots as Greg King, calling him a “dedicated aviator and a dear friend to many of us.”

King had served alongside the division on wildland fires in Alaska, and his loved ones are currently employed with the agency, it said.

“We are mourning both pilots who bravely supported firefighting efforts, and our hearts go out to their families,” the Alaska Division of Forestry & Fire Protection said in a statement on Monday. “We are standing alongside our staff and Greg’s loved ones as we grieve this profound tragedy together.”

The identity of the second pilot is being withheld pending next-of-kin notifications, the agency said.

The FAA and National Transportation Safety Board are investigating the crash. The cause remains unknown at this time, Cossel said.

Nearly 600 ground and air personnel have been assigned to the Dome Fire, which is burning in the wilderness northeast of Wawona, park officials said.

The fire has burned more than 3,200 acres since igniting on Sept. 15 and was 15% contained as of midday Monday, fire officials said. The terrain is extremely rugged and steep, making it challenging for firefighters to get to, Cossel said.

“The Dome Fire continued to spread at a moderate rate of growth,” the National Park Service said Monday. “Fire behavior will remain moderate, with spotting behavior being a big challenge in the full suppression efforts of this fire.”

The cause of the fire remains under investigation.

Yosemite National Park remains open, though some trails are closed due to the fire.