Himesh Lal Karna, an air traffic control officer at Kathmandu’s Tribhuvan airport, said on Monday that the rescuers reported no-one survived the crash.
"The seven-member rescue team found the crashed helicopter and called us. They said there were no survivors," Karna said.
The rescuers said they saw many bodies at the site, but Minraj Upadhyaya of Nepal's civil aviation authority said only one could be identified.
The army helicopter found the crashed aircraft one nautical mile southwest of Ghunsa, a village in Taplejung district, about 300km east of the Nepalese capital, Kathmandu.
"The army helicopter could not land at the site but it could see many bodies there," Purushottam Shakya, who coordinates rescue operations from Kathmandu airport, told Reuters.
"The rescuers were not able to have a close view because of the terrain," he said.
"We have sent a medical team and photographers to take pictures and are waiting for more details."
The search for the missing Russian-made helicopter had been hampered by rains and fog which prevented rescue helicopters taking off.
"The rescuers were not able to have a close view because of the terrain," he said"
Purushottam Shakya, coordinator of the rescue operation
The area, located above 3,500 metres (11,480 feet), is very remote and with few villages, in a rugged landscape dominated by ravines and gorges, officials said.
Of the 20 passengers and four crew members, 17 were Nepalis. Others included a Finnish diplomat, two Americans, a Canadian, an Australian and two Russians.
Gopal Rai, Nepal's junior forest minister, and his wife, Pauli Mustonen, the Finnish Charge d'Affaires, and Margaret Alexander, the deputy director of the United States Agency for International Development (USAID) in Nepal, were among them.
Other passengers were conservationists working for the WWF and two Nepali television journalists.
The passengers had attended the handover of a WWF project to the local community and were on their way back when the helicopter went missing.
Officials said on Sunday that villagers had reported hearing a loud noise in a gorge soon after the helicopter left Ghunsa, a region that is home to the world's third-highest peak, Mount Kanchenjunga.
Eighteen people, including 13 Germans, were killed when a commercial plane crashed in the hills of western Nepal in 2002.
Himalayan Nepal, home to Mount Everest, has a poorly developed road network and many tourists and officials travel by helicopters or small planes to remote mountainous areas.