WASHINGTON (Reuters) - U.S. officials on Tuesday were investigating the cause of a military transport plane crash that killed 16 service members including elite special operations forces a day earlier, leaving a miles-long trail of wreckage in rural northern Mississippi.

The KC-130 Hercules aircraft disappeared from air traffic control radar over Mississippi after taking off from Cherry Point, North Carolina. It plunged into a soybean field at about 4 p.m. CDT (5 p.m. EST) on Monday in Mississippi’s LeFlore County, about 100 miles (160 km) north of Jackson, the state capital.

Fifteen Marines and one Navy sailor were killed, the U.S. Marine Corps said. The names of the deceased were being withheld until family members were notified. Further details were not released. Gen. Robert Neller, Commandant of the Marine Corps, pledged “a thorough investigation into the cause of this tragedy.”

The aircraft was originally based out of New York’s Stewart Air National Guard Base, Marine Corps officials said.

It was transporting equipment and people to a Navy facility in El Centro, California. Equipment on board included small arms ammunition and personal weapons.

Seven of the 16 who perished, including the sailor, were based at Camp Lejeune in North Carolina and were members of the elite Special Operations Command of the Marine Corps.

The Poughkeepsie Journal in New York said Marine reservists from the nearby Stewart Air National Guard Base were also on the plane.

U.S. President Donald Trump said on Twitter that the crash was heartbreaking. “Melania and I send our deepest condolences to all!” he wrote.

Stars and Stripes, which covers U.S. military affairs, reported that witnesses said bodies were found a mile from the wreckage.

Images posted online by local media showed the plane’s crumpled remains engulfed in flames in a field surrounded by tall vegetation, with a large plume of smoke in the sky.

The crash left a five-mile (8-km) trail of debris, the local Clarion-Ledger newspaper reported.

The KC-130 Hercules, manufactured by Lockheed Martin Corp LMT.N, conducts air-to-air refueling, carries cargo and performs tactical passenger missions. It is operated by three crew members and can carry 92 ground troops or 64 paratroopers, according to a Navy website.

Greenwood Fire Department Chief Marcus Banks told the Greenwood Commonwealth newspaper that firefighters were driven back by several “high-intensity explosions” that may have been caused by ammunition igniting.

It was the worst Marine Corps aviation crash since January 2005, when a CH-53E crashed in Iraq, killing 30 Marines and one sailor.