A US search team identified the wreckage as that of the missing Marines UH-1Y Huey helicopter deployed after the Himalayan state was hit by a massive earthquake last month that killed more than 8,000 people.
Crash debris was found 13km north of the town of Charikot near dense forest and rugged terrain.
"It was a very severe crash. We believe there were no survivors," said John Wissler, lieutenant general of the US Marines.
The Huey went missing while it was distributing aid on Tuesday, the day a strong aftershock hit Nepal and killed more than 100 people.
Six Marines and two Nepali soldiers were on board when it went missing, after the crew was heard over the radio saying the aircraft was experiencing a fuel problem.
US Defense Secretary Ash Carter mourned the loss of the Marines, and a Pentagon spokesman said US officials were in touch with the families.
"This tragedy is a reminder of the vital but dangerous role that American servicemembers play in delivering humanitarian assistance and disaster relief," Carter said in a statement.
The Huey, an iconic helicopter dating back to the Vietnam War era, was completely destroyed, Nepal's top defence ministry official said earlier on Friday.
"As the helicopter has broken into pieces and totally crashed there is no chance of any survivors," Nepal's defence secretary Ishwori Prasad Paudyal.
HUNDREDS IN SEARCH
After a three-day search the Huey was spotted near the village of Ghorthali at an altitude of 11,200 ft (3,400 m), an army general told Reuters earlier, as helicopters and Nepali ground troops converged on the crash site.
"It was found on a steep slope," Major General Binoj Basnet said. US and Nepali teams investigated the site on Friday in an attempt to determine the cause of the crash.
On Saturday, US and Nepalese aircraft plan to get their rescue team back up to the site to collect the bodies and begin identification of the charred remains.
The area's tallest peak soars to more than 7,000 metres (23,000 ft). Hillsides are cloaked with lush forest that made it hard to find the chopper even though it came down just a few miles from Charikot, the capital of Dolakha district that lies half a day's drive to the east of Kathmandu.
An army base in the town has been serving as a hub for operations to airlift and treat those injured in the two earthquakes, and Prime Minister Sushil Koirala flew in on Thursday for an on-the-spot briefing.
The first quake, which struck on April 25 with a magnitude of 7.8, has killed 8,199 people. The death toll from a 7.3 aftershock on Tuesday has reached 117, with many victims in Dolakha.
The combined toll is approaching the number of just over 8,500 who died in an earthquake in 1934, the worst natural disaster on record to hit Nepal.
Some 76,000 more have been injured, while hundreds of thousands of buildings, including ancient temples and monuments, have been damaged or destroyed. Nearly three weeks after the first quake, aftershocks continue to rattle the country.
Nepal mobilised 600 soldiers to search for the missing Huey.
Two more US Hueys, two MV-22B Osprey tilt-rotor planes, and Nepali and Indian choppers had been involved in the search for the helicopter, which was part of a joint task force sent in by the United States to provide assistance at Nepal's request.
US officials said the crash would not affect ongoing relief operations.
"We will continue to stand by Nepal as long as they need our help," Wissler told reporters.
