A land mine exploded under a packed bus in southern Nepal on Monday, killing 38 passengers and wounding 72 in one of the worst attacks on civilians since a Maoist rebellion erupted in 1996.

The rebels, who are trying to topple the monarchy and establish one-party communist rule in the poor Himalayan kingdom, are not generally known to target civilians. But army officers said they were to blame.

"The bus ran over a land mine planted by the terrorists," an army officer said, referring to the Maoists.

"The place is littered with blood, limbs are scattered around the site. . . . Many women and children have been killed," he said by phone from the area.

The explosion took place by the side of a river in Madi village in the Maoist stronghold of Chitwan district, about 95 miles southwest of Katmandu, officials said.

Some of the most seriously wounded were evacuated by helicopter to Katmandu; others were treated at a local hospital. "Security has been stepped up in the area and an extensive search for the terrorists has been launched," an army official said.

The commuter bus was packed with villagers, with many traveling on its roof, when the land mine exploded, residents said. Many of the passengers were headed to work or local markets.

A Reuters photographer who visited the site eight hours after the blast saw dismembered bodies, many of which were the remains of women and children, lined up on one side of the dusty road.

Witnesses said the blast hurled the bus several feet in the air. There was a deep crater on the road.

An army officer at the site said rebels detonated the mine with a remote-control device from the top of a tree about 250 yards away.

There was no immediate claim of responsibility.

About 12,000 people have been killed in the nine-year insurgency, which has ravaged Nepal's tourism-dependent economy and forced tens of thousands of people to flee their homes.