(CNN) Seven of the service members killed in a military transport plane crash in Mississippi were from an elite Marine unit based at Camp Lejeune, North Carolina, the Marine Corps said Tuesday.
The other nine Marines killed were from Orange County, New York, county executive Steve Neuhaus said. The KC-130T aircraft was based in New York, officials said.
Investigators are trying to determine why the plane crashed in western Mississippi's Leflore County on Monday afternoon, Maj. Andrew Aranda said.
The transport plane, carrying fifteen Marines and a Navy corpsman, was moving personnel and equipment from North Carolina to a western base to train before deploying, the Marine Corps said.
Six Marines and the sailor were members of the 2d Marine Raider Battalion, based in Camp Lejeune in Jacksonville, North Carolina. They were part of Marine Corps Forces, Special Operations Command and were traveling to the Marine Corps Air Station in Yuma, Arizona, for small unit pre-deployment training.
"The incredible demands of this dangerous and demanding calling forge some of the tightest units and family bonds found in the US military," special operations command said. "This loss impacts us all."
Neuhaus said the New York-based Marines will be flown back to Dover Air Force Base, then to Orange County.
The names of the deceased weren't immediately released, but a father of one of the Marines told CNN affiliate WCAX his son was on the plane.
Gunnery Sgt. Brendan Johnson was from Vermont. His father told WCAX and CNN that his son loved his job.
"He thought it was one of the best jobs in the Marine Corps. He really loved flying. He loved going different places," Kevin Johnson said of his son, who spent 23 years in the Marines and was a loadmaster.
Brendan Johnson, 45, planned to retire next year, after a career that took him to Europe, Africa, South Asia and the Pacific, including deployments to Afghanistan and Iraq.
"He was looking forward to retiring, he said it's time to let the younger kids do this," his father said.
The aircraft belonged to a Marine Forces Reserve refueling and transport squadron based at Stewart Air National Guard Base in Newburgh, New York.
The plane, which the military can use to refuel planes in the air and carry cargo, went down in a rural area just off US 82, about 85 miles north of Jackson, with debris found on both sides of the highway, CNN affiliate WDBD reported.
The flight originated from Marine Corps Air Station Cherry Point in eastern North Carolina.
Federal Aviation Administration officials contacted the Marines when the aircraft disappeared from air traffic control radar over Mississippi, officials said.
"Every resource we can pull from will be used to determine what happened," Aranda told reporters a couple miles from the crash site.
Because the plane was carrying small-arms ammunition and weapons, an explosive ordnance disposal team was at the crash site, military officials said.
"Out of precaution, we just wanted to make sure people do not approach ... just out of general safety," Aranda said.
Flames and dark smoke rose from part of the wreckage in a field off the highway, video from WDBD on Monday showed.
CNN affiliates WDBD and WHBQ, citing officials they didn't name, reported the plane had stopped in Memphis, Tennessee. Aranda did not confirm that, saying he didn't know details about the aircraft's flight plan.
A witness to Monday's crash, Andy Jones, said he heard a loud bang while working in a field near his catfish farm.
The plane spiraled, nose down, to the ground, Jones said. One of the engines appeared to be trailing white smoke, he said.
"At first it looked like an acrobatic plane, like a stunt plane, blowing the smoke out the back" he said. "Then all of a sudden you realized that the smoke was coming off one of sides of the wing."
He called 911 after the crash. Jones said he didn't see the impact because trees blocked his view.
He said he went out to the site and saw a bunch of mini-explosions coming from the crash.
President Donald Trump called the crash "heartbreaking."
"Melania and I send our deepest condolences to all!" the President tweeted.
Near the crash site on Tuesday morning, David Weeks stopped along US 82 and played taps on a bugle, video from CNN affiliate WJTV shows.
Weeks, of Inverness, Mississippi, told CNN that he did it "to let these American heroes know their service and sacrifices were appreciated." He is a member of the Patriot Guard Riders, a nonprofit motorcycle group that honors fallen troops.
"Playing taps was my way of saying, 'thank you,'" he told CNN.
The Marines' commandant expressed his "deepest condolences to the families of those killed in the aircraft mishap yesterday afternoon in Mississippi."
"Please keep the families of our 16 fallen service members in your thoughts and prayers," Gen. Robert Neller said.
Interior Secretary Ryan Zinke, who had long service as a Navy SEAL, was among officials posting condolences on social media. "Please join me in praying for or sending good thoughts to the families and unit of the Marines we lost tonight in the C 130 crash," Zinke wrote on Twitter.
U.S. Sen. Thad Cochran, R-Mississippi, posted on Twitter: "Deeply saddened by the loss of life in today's @USMC KC-130 crash in the Mississippi Delta. Our thoughts & prayers are w/everyone involved."
Often used for airborne refueling, the KC-130, made by Lockheed Martin Corp., also can be used to deliver cargo, troops and equipment.
The first KC-130s appeared in 1962. Its normal range of 1,150 miles as a tanker and 3,200 miles on cargo missions gives it access to the entire war arena.
The maximum takeoff weight for the KC-130T is 175,000 pounds and its flight ceiling is 25,600 feet.
One of the most recent crashes of a US C-130 cargo plane happened in October 2015, when one went down 28 seconds after takeoff from Afghanistan's Jalalabad Airport near the Pakistani border as it was heading to Bagram Airfield. The crash killed 14 people.
A US Air Force investigation blamed the crash of the C-130J on the misuse of a night-vision goggles case that the pilot had placed in front of the cockpit yoke while the plane was on the ground.
The pilot put the case there to prop up part of the plane's tail to help the loading team deal with some tall cargo, but the case was never removed, and when the plane's nose pitched up too far, the case blocked the yoke when the pilot tried to move it forward, the investigation report said.
Correction: An earlier version of this story incorrectly reported the FBI is at the scene of the crash. The FBI told CNN on Tuesday that it is not at the scene.