The army said on Saturday that the deaths took place in a firefight in Syangja, a Maoist stronghold 225km west of the capital, Kathmandu, two days after soldiers shot and killed 10 rebels in the same area.
An army officer said: "Details of the clash are awaited. A search is continuing."
Last Wednesday, a fierce battle erupted between government forces and the rebels in the western town of Dhangadhi, leaving at least seven policemen missing.
The clashes erupted after the rebels attacked many government installations.
The Maoists have been fighting since 1996 to replace the monarchy with a communist republic in the world's only Hindu kingdom, a conflict that has cost more than 12,500 lives and shattered the Himalayan kingdom's tourist and aid-dependent economy.
On 2 January, the rebels ended a four-month truce, accusing the royalist government, which had refused to match the truce, of provoking them to break it.