Nepalese police have fired tear gas and rubber bullets at thousands of protesters who tried to march on King Gyanendra's palace in Kathmandu.
Police threw a tight cordon around the centre of the city
Hospital officials say at least 150 people were injured as about 100,000 Nepalis defied a curfew and security cordons to march into the capital.
The clashes came a day after the king offered to restore democracy.
Protesters rejected his offer as inadequate and the opposition declined his call to form an interim government.
Tens of thousands of demonstrators began heading towards central Kathmandu early on Saturday, ignoring an eight-hour, shoot-on-sight curfew.
"We want a republic, We don't want the king any more," the crowds chanted.
They brushed past police and army lines before reaching an inner cordon where soldiers in armoured vehicles and long lines of riot police held firm.
The security forces used robust and at times brutal tactics to push people back, the BBC's Nick Bryant reports from the capital.
Two people were critically injured in one exchange alone, our correspondent says.
Sammu Pratap Rana was one of the protesters caught up in a baton charge by police.
"We were marching along peacefully, when suddenly the police fired tear gas shots. I turned and ran," he told BBC News.
"Then I fell and a policeman hit me on the back with a baton."
Violence was also reported in other areas of the city.
The Associated Press news agency said that the Norvic hospital in the Thapathali neighbourhood was full of people seeking treatment.
Doctors there said at least four people had been hurt by bullets and more than 40 were injured in baton charges.
At Kathmandu's Model Hospital, doctors said dozens of people had been hurt, most by tear gas but some with bullet wounds, Reuters reported.
The authorities have now cut off the mobile phone network.
After more than two weeks of protests and at least 14 violent deaths, the beleaguered monarch gave a nationwide speech on Friday to announce that he intended to restore power to the people.
"Executive power of the kingdom of Nepal, which was in our safekeeping, shall from this day be returned to the people," he said.
He called on opposition parties to put forward their candidate for prime minister.
But after meeting on Saturday, the seven-party opposition alliance rejected the king's offer.
"We will not accept...We will continue the protests," Madhav Kumar Nepal, general secretary of Communist Party of Nepal told cheering supporters in Kathmandu.
The opposition parties complained that the king had failed to address some of their most basic demands, not least the creation of a constituent assembly to decide the future of the monarch.
The general strike that has brought most of the country to an economic standstill is also continuing.
Great hostility is now being directed against King Gyanendra, partly because of his stubborn intransigence but mainly because of his bloody tactics, our correspondent says.
Many protesters will not be satisfied until the king has given up his throne, he adds.
India, which holds considerable influence over Nepal, said the king's move "should now pave the way for the restoration of political stability and economic recovery".
US state department spokesman Sean McCormack said: "We expect the king to live up to his words... We urge the parties to respond quickly by choosing a prime minister."