Though no-one has claimed responsibility for the attacks, local police say they are likely to be the work of the rebels, who called an end to their ceasefire on 27 August.
“We are waiting for a detailed report on the incident,” an army source told AFP.
Nepal is fighting a war against a Maoist revolt which seeks to replace the constitutional monarchy with a communist republic.
The rebels walked away from peace negotiations in August when the government rejected their demand for a new constitution to define the role of the king.
In a separate incident, as many as 100 Maoist rebels may have been slain in a battle with security forces in western Nepal.
There is no independent way of verifying the toll, though military sources quoted eye-witness accounts of fighting near the village of Sini in Achham district.
The state-run English daily newspaper, The Rising Nepal, also said up to 100 guerrillas could have died, quoting the Achham District Administration Office.
“Eyewitnesses said the Maoists had carried away the bodies of their dead in bamboo baskets or simply chopped off their heads to conceal their identities,” the paper reported.
Rebel violence has increased since the end of the ceasefire, which lasted seven months. As many as 184 people have died since then.
The rebels have been fighting for a communist republic in Nepal since 1996 and the insurgency has claimed more than 7,800 lives.