A spokesman for the Emergencies Ministry said "several parts of the pilots' bodies" had been found, RIA Novosti reported.
The KC-135 Stratotanker crashed Friday just after taking off from Manas Airport, a provincial airfield used by the U.S. military for support operations for Afghanistan, The New York Times reported. AKI Press, a local news agency, said witnesses described an explosion followed by the breakup of the plane.
Forty rescue workers were searching for debris from the Boeing KC-135 refueling aircraft, which is scattered over a 2-1/2-mile area about 6 miles from the Kazakhstan border.
The plane was carrying three Americans and about 70 tons of fuel when it crashed into a mountain gorge. Officials said the cause of the crash had not been determined Saturday and the black box recorders had not been found.
Preliminary findings of a special commission set up to investigate the crash were expected in three or four days, said Transport and Communications Minister Kalyhbek Sultanov, head of the commission.
The Stratotanker is used for in-air refueling in Afghanistan. A fleet of the planes has been based at Manas for more than a decade.