Twenty people have been killed in a clash in central Nepal, officials say.
Six security forces and 14 Maoist rebels were found dead following an attack on an army patrol on Saturday night, the army said.
Meanwhile Nepalese opposition parties called for three more days of protests after scores of people were arrested in clashes in the capital on Saturday.
"There will be no break in the struggle for democracy" said Madhav Kumar Nepal, of the Communist Party of Nepal.
An opposition co-ordination committee also announced a general strike that will be held nationwide on Thursday.
An alliance of seven parties is demanding that King Gyanendra give up the absolute power he seized last year.
House arrest
The opposition wants its supporters to boycott local elections next month, which it says are undemocratic and aimed at entrenching the king's direct rule.
Hundreds of people have been arrested in the past few days.
On Friday security forces detained scores of people, and put five opposition leaders under house arrest, to pre-empt planned rallies.
Nepal's authorities said the arrests followed information that Maoist rebels were planning to infiltrate the rally and incite violence.
Then on Saturday, impromptu protests on the streets of Kathmandu led to clashes with police.
Activists threw stones at police lines. Police responded with tear gas and baton charges.
The government said nearly 200 people were taken away in trucks on Saturday, but the opposition put the number much higher.
Poor conditions
There has been strong condemnation of the arrests from the international community, and calls for a return to democracy.
A member of Nepal's official human rights body has expressed concern at the conditions in which detainees are being held.
Sudip Pathak, who sits on the National Human Rights Commission, an independent but statutory body appointed by the government, told the BBC he had visited detention sites.
He said he found 40 men to a room, inadequate medical facilities, no drinkable water and very poor food.
The clash on Saturday night that left 20 people dead was the bloodiest since Maoist insurgents abandoned a four-month unilateral truce earlier this month.
Sixty people have been killed in escalating violence this month.
More than 12,000 people have died in Nepal since the Maoists began their fight for a communist republic 10 years ago.
PHOTO CAPTION
Nepalese soldiers. Suspected Maoist rebels killed five police and seriously wounded three when they attacked two police checkposts in mid-western Nepal, a police official said. (AFP)