Fragments of the aircraft, a Boeing KC-135 refueling plane known as the Stratotanker, were said to be scattered over a half-mile area, ITAR-Tass reported.
The plane typically carries three crewmembers, a pilot, co-pilot and boom operator, the Russian news agency RIA-Novosti said.
A rescuer said part of a parachute had been found.
Azamat Mambetov, an official of Kyrgyzstan's emergency ministry, said people reported seeing a plane disintegrate before crashing into mountains near the village of Chorbolu, adding rescue crews were immediately sent to the area where the crash was reported.
The plane had left a U.S. air base at Manas International Airport near Bishkek, Kyrgyzstan, and was en route to Afghanistan, the Los Angeles Times reported.
An airport employee said the crew reported bad weather and thunder in the area, and asked to fly around towering cumulus clouds on the route.