State radio said on Thursday the rebels were killed when government troops stormed a Maoist guerrilla training camp in Achham, 500km west of the capital Kathmandu.
There was no comment from the rebels. More than 100 people, mostly rebels, have died since the Maoists ended a temporary festival truce a week ago, the government said.
Nepali state radio said seven rebels were killed in another clash on Wednesday in Dang district, also in the western part of the country.
The Maoists have been battling government forces since 1996, with a view to ending the country's constitutional monarchy and establishing a communist republic.
In August, the rebels walked out of talks after the government rejected their demand for a new constitution.
The seven-year insurgency has claimed more than 7600 lives.