A U.S. service member and three defense contractors died Thursday when a U.S. military-contracted plane crashed in a rice field in the southern Philippines, according to U.S. Indo-Pacific Command. The aircraft was conducting an intelligence, surveillance, and reconnaissance mission at the request of Philippine allies when it went down in Maguindanao del Sur province. The cause of the crash remains under investigation.

The remains of the plane crash in Maguindanao del Sur, Philippines.

Local officials confirmed that the wreckage was found in Ampatuan town, where all four victims were recovered. Residents reported seeing smoke and hearing an explosion before the plane plummeted about half a mile from a group of farmhouses. No injuries were reported on the ground, though a water buffalo was killed in the crash. The area has since been secured by troops.

U.S. forces have long operated in the Philippines, providing advisory and training support to local troops fighting militant groups in the country’s predominantly Muslim southern region. The victims’ identities are being withheld until their families are notified.