Demonstrators have taken to the streets of Kathmandu in protest at Nepali King Gyanendra's absolute power.
Police confronted the activists, who defied a new ban on rallies.
Some of the pro-democracy protesters hurled stones, in what correspondents described as a rally with a bitter atmosphere.
Many were bundled into police trucks.
Both activists and police were reportedly injured in the clashes.
Residents looked worried as the violence escalated after a crackdown on activists on Friday.