Nepalese riot police used tear gas and batons against students on the streets of Kathmandu as protests against King Gyanendra entered their 18th day.
The protesters want the king to reinstate parliament
They are continuing despite a ban on public gatherings of over five people.
At least a dozen people were injured and hundreds arrested in the capital and thousands were reported to have demonstrated in provincial towns too.
Nepal has seen regular protests since the king suspended parliament and chose his own cabinet two years ago.
The BBC's Charles Haviland in Kathmandu says the ban seems to have stoked fresh anger and that a slightly new level of bitterness was felt on the streets.
Students from Kathmandu's leading Tribhuvan university hurled bricks and stones at police that had arrived to disperse them.
The police responded by firing tear-gas canisters and baton-charging the crowd.
Police also broke up rallies on Saturday
Despite heavy rain, the stench of tyres burnt by students filled the air.
Our correspondent says most of the demonstrators seem to be committed opposition party people - who demand the king restores the suspended parliament and an all-party government.
Some reports said Sunday's demonstrators were protesting, in part, against the detention of around 2,000 people by the police on Saturday.
Hundreds of protesters have been arrested and released by the police every day over the past fortnight, our correspondent says. Waiting police trucks often whisk them away as soon as they arrive.
Nepal's government imposed a ban on protests in Kathmandu 10 days ago on the grounds they might be infiltrated by Maoist rebels.
A rebel army of peasants, led by left-wing ideologues, has been waging an eight-year-old uprising in Nepal, which has left an estimated 8,000 people dead.
They want the monarchy abolished in favour of a communist republic and are apparently not linked to the opposition protesters in the capital.