The policemen were on a search mission for Maoist hideouts in the insurgency-torn southwestern Nepalgunj district when their truck was blown up by underground explosives, police said.

"Two of the 21 policemen who died were of high rank. The Maoists disappeared after the attack," senior police officer Ravi Raj Thapa told AFP.

He said 13 of the injured policemen were airlifted to a hospital in the capital Kathmandu, 440km away, and three others were treated locally after the ambush in Khairikhola village.

It was the deadliest attack in Nepal since King Gyanendra on June 3 swore back in Prime Minister Sher Bahadur Deuba, whom he had fired two years earlier and replaced with a handpicked royalist government.

The king had accused Deuba in 2002 of "incompetence" at fighting the Maoists, who have taken control of much of the countryside in their "people's war" aimed at ending the monarchy and establishing a communist state.

The civil war has claimed more than 9,500 lives since 1996 and devastated the Himalayan kingdom's fragile tourism-dependent economy.

Deuba on June 9 used his first national address since his reappointment to appeal to the Maoists to come to the peace table, promising "maximum flexibility" in negotiations.

PTI adds: The Maoists exploded a powerful bomb at the house of a top police officer in Central Nepal, even as they abducted nearly 200 students from eight schools in East Nepal.

The single-story house belonging to Deputy Inspector General of Police, Devendra Bahadur Malla, situated in Gauriganj area in Chitawan district in central Nepal was completely damaged by the explosion triggered by the Maoists on Sunday, according to state-run The Rising Nepal.

However, no one was injured in the incident.

The Maoists have abducted 197 students below the age of 18 from eight different schools at Udayapur district in east Nepal, according to state-run Gorkhapatra daily.

(AFP/ PTI)