At least 150 anti-government protesters have been arrested in Nepal's capital, Kathmandu, as a campaign against King Gyanendra gathers pace.
The protesters want the king to step down
Police fired tear gas and used batons to disperse demonstrators, who hurled stones and set fire to a post office.
The unrest came on the second day of a strike called by the opposition against the king, who sacked the government and introduced the direct rule last year.
He has come under widespread criticism over the crackdown on the opposition.
Hundreds of people have been arrested since the four-day strike began on Thursday.
Hundreds of stone-pelting protesters took to Kathmandu's narrow streets, setting fire to the post office and vandalising taxis.
They shouted that the king was a thief and should leave the country, the BBC's Charles Haviland in Kathmandu reports.
Many of those rallying appeared to be students supporting the opposition parties, our correspondent says.
Fierce clashes broke out when police in riot gear used tear gas and batons to break up the action.
Clashes also were reported in several other towns of the kingdom.
"This is the final push of the movement. The days of the king are numbered," Sova Sapkota, an activist with the Communist Party of Nepal (Unified Marxist Leninist), was quoted as saying by the AFP news agency.
"We will continue to defy the ban order," she said.
'Need for peace'
Meanwhile, King Gyanendra has stressed the need for peace.
"Let us all pledge today to devote time for establishing permanent peace," he told an international conference of Hindus in southern Nepal.
However, he made no direct reference to the Maoist violence or the street protests by the opposition parties.
King Gyanendra has said he was forced to seize power in February 2005 because of the growing Maoist insurgency that has killed more than 10,000 people since 1996.
The latest protest has been organised by Nepal's seven-party opposition alliance.
A mass anti-monarchy rally is planned for Saturday, despite a ban on public protests in Kathmandu.