Nepali police arrested hundreds of people on Friday, including political leaders, as thousands chanting anti-monarchy slogans defied a ban on rallies and took to the streets in protest against the king.
"Riot police detained nearly 1,000 protesters and took them away... in trucks," Krishna Sitaula, a member of the biggest opposition party, Nepali Congress, told Reuters.
"Down with absolute monarchy!" some demonstrators shouted before they were hauled away. Sitaula said former Congress prime minister Girija Prasad Koirala was injured as his supporters clashed with police to stop him being detained.
About 30,000 people joined the protest, large by Nepali standards but well short of the 200,000 organisers had hoped for before Thursday night's sudden ban on public gatherings.
The non-elected government, appointed by King Gyanendra, outlawed meetings of five or more people in the capital and surrounding areas, saying it had information Maoist revolutionaries planned to use the protests to incite violence.
Friday's rally marked the anniversary of the main 1990 protests that ended decades of absolute monarchy in Nepal.