Nine soldiers have been killed after two US army helicopters crashed in Kentucky, according to an official.
Crew members were flying the HH-60 Blackhawk helicopters during a routine training mission before the fatal incident in Cadiz, Trigg County, the Fort Campbell army base said in a statement.
One aircraft had five soldiers while the other had four - all those on board died.
"Right now our focus is on the soldiers and their families who were involved," the statement added.
The training exercise involved night vision goggles, said the army. The cause of the crash is not yet known.
US army secretary Christine Wormuth called it a "heavy day" for the military.
The two aircraft crashed about 30 miles (48km) northwest of Fort Campbell around 10pm local time on Wednesday (3am on Thursday UK time).
"The crash occurred in a field, some wooded area," Kentucky state police trooper Sarah Burgess said.
"At this time, there are no reports of residence damage."
The incident is now being investigated.
'We saw a huge glow like a fireball'
Local resident Nick Tomaszewski, who lives about a mile from the crash scene, said he saw two helicopters fly over his house moments before the tragedy.
"For whatever reason last night my wife and I were sitting there looking out on the back deck and I said, 'Wow, those two helicopters look low and they look kind of close to one another tonight'," he said.
The aircraft flew over and looped back around and moments later "we saw what looked like a firework [going] off in the sky".
"All of the lights in their helicopter went out... then we saw a huge glow like a fireball," he added.
Flyovers for training exercises take place almost daily and the helicopters usually fly low but not so close together, Mr Tomaszewski continued.
The helicopters involved were from the 101st Airborne Division which is known as the "Screaming Eagles".
The HH-60 is a variant of the Black Hawk helicopter designed to provide support for various military operations, including air assaults and medical evacuations, according to the army.