Indian Prime Minister Manmohan Singh has told parliament that the hunger strike by the anti-corruption activist, Anna Hazare, is "totally misconceived".
He said the 74-year-old was trying to circumvent democracy by demanding an overhaul of anti-corruption legislation.
Mr Hazare has rejected an offer by the state to free him from a jail in Delhi.
He says he will remain in prison unless he can continue the protest stopped by his arrest on Tuesday.
Protests backing his campaign have been gathering momentum across the country.
Hundreds of supporters have gathered outside the jail, many carrying the Indian flag and shouting "Down with corruption" and "Hail Mother India".
Supreme Court lawyers have announced they will march to show their support for Mr Hazare, while auto-rickshaw drivers have gone on strike.
'Grave consequences'
Mr Hazare and at least 1,200 of his supporters were arrested at a park in the capital on Tuesday morning, hours before he was due to begin his "fast unto death".
The government denied it was stifling a democratic protest, saying the protesters had been detained because they had not accepted the police's restrictions on the number of fasting days and participants.
As public anger mounted, officials ordered Mr Hazare's release. But he refused to leave jail before the police dropped the conditions they set for his freedom.
However, there is no sign yet that the government is prepared to allow that to happen, says the BBC's Mark Dummett in Delhi.
Speaking in parliament, Mr Singh argued that the arrests had been justified and that Mr Hazare's campaign amounted to a challenge to the authority of the government, which he was duty bound to protect.
"I acknowledge that Anna Hazare may be inspired by high ideals," he said. "However, the path that he has chosen to impose a draft of the bill on parliament is totally misconceived and fraught with grave consequences for our parliamentary democracy.
"Those who believe that their voice and their voice alone represents the will of 1.2 billion people should reflect deeply on that position.
"They must allow the elected representatives of the people in parliament to do the job that they were elected for."
The prime minister's speech was constantly interrupted by opposition MPs, many of whom jeered and shouted "shame".
Our correspondent says a prolonged stand-off between the two sides looks possible, with demonstrations being held in Delhi and a number of other cities, and the government's options looking limited.
'Fundamental right'
Mr Hazare is reported to have spent Tuesday night at one of the rooms in the administrative block of Tihar jail.
A member of the India Against Corruption (IAC) movement, Gaurav Bakshi, told the BBC that Mr Hazare was determined to continue to his hunger strike.
"He must be allowed to sit the fast that he was originally asking for at JP Park with no conditions attached to it," he said.
"His basic fundamental reason is that his fundamental right as a citizen of the country - the freedom to fast and protest in any manner anywhere in the country peacefully - has been taken away with 22 conditions imposed. He is against that and he is continuing with the fast where he is."
Mr Bakshi said he had the support of Indians all over the world, who realised this was an "opportunity to clean up the country".
"I think the entire country is sick and tired of essentially fools leading this country. The people have had enough," he added.
Mr Hazare has called the proposed anti-graft legislation a "cruel joke" and has described the fight against corruption as the "second war of independence".
He says the new anti-corruption ombudsman - Lokpal - should be able to investigate anyone, including the prime minister and senior judges.
India has recently been hit by a string of high-profile corruption scandals, including a multi-billion dollar alleged telecoms scam, alleged financial malpractices in connection with the Delhi 2010 Commonwealth Games and allegations that houses for war widows were diverted to civil servants.
Critics of the government say the scandals point to a pervasive culture of corruption in Mr Singh's administration.
A recent survey said corruption in Asia's third largest economy had cost billions of dollars and threatened to derail growth.
