The official said the aircraft went down near al Qaim in western Anbar Province. USA forces provide surveillance, intelligence and air support to Iraqi-led military missions, US officials have said.
The aircraft, a HH-60 Pave Hawk helicopter, was not on a combat mission at the time of the tragedy.
An accompanying USA helicopter immediately reported the crash and a quick reaction force comprised of Iraqi and coalition service members secured the scene.
"It was a routine troop transport operation going from Iraq to Syria, nothing out of the ordinary", the official said.
The names of those killed - everyone on board - will be released after next of kin have been notified, the statement added. Gen. Jonathan P. Braga, director of operations in the fight against IS in Iraq and Syria.
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US forces and Iraqi partners have been winding down their operations against the Islamic State, but fighters pushed from urban centers in Iraq have escaped to the desert along the border to hide.
The cause of the crash is under investigation.
Prime Minister Haider al-Abadi declared victory over ISIS in Mosul in July.
The town is about two and a half hours from Deir Ezzor, a Syrian city where USA forces last month carried out airstrikes on Syrian pro-government forces. In November, Iraqi forces retook the last Iraqi town held by ISIS - Rawah, near the border with Syria.
The US acknowledges that it has about 5,200 troops in Iraq that are part of a coalition fighting Islamic State militants.