At least 35 Maoist rebels have died in an attack on a Nepalese police post ending a nine-day ceasefire, according to officials.
At least three policemen were also killed when the rebels tried to overrun the compound in Khas-Kusum, near the western town of Dang.
The fierce gun battle, which began late on Friday, continued until Saturday morning, police say.
The clash puts an end to a nine-day truce declared by the rebels for the Hindu festival of Dashain.
Violence did not stop during the ceasefire. Eight people were reported killed in separate clashes between the security forces and the rebels on Thursday.
There has been a surge in fighting since peace talks between the government and rebels broke down in August.
Nearly 8,000 people have died since the Maoist rebels launched their armed struggle in 1996 to replace Nepal's monarchy with a communist republic.