Maoist rebels, fighting against Nepal's constitutional monarchy, set off a bomb under an army truck in Makawanpur district killing four soldiers and wounding 11 others, an army official said on Friday.

Makawanpur, 150km south of Kathmandu, is a stronghold of the Maoist rebels campaigning for a communist republic in the world's only Hindu kingdom.

"Four soldiers died and the injured have been shifted to a hospital in Kathmandu in a helicopter," he said.

In a separate incident, two Maoists were killed in a gunbattle with soldiers in Morang in east Nepal.

Violence has surged in the country since the rebels walked out of peace talks in August after the government refused the rebel demand for a new constitution to decide the future of
Nepal's monarchy.

More than 8500 people have died in the conflict - 1300 of them since August - that has also crippled the economy and hit tourism, a key source of income.