Indian Prime Minister Manmohan Singh invited rival party leaders to gather on Wednesday as the government struggles to handle a groundswell of passionate support for Anna Hazare, a veteran campaigner who is on public fast in central New Delhi.

Hazare has been refusing food for a week to demand changes to an anti-corruption bill before parliament, and his protest has triggered demonstrations across India.

Singh's Congress party-led government, which has been hit by a series of graft scandals, has appeared out of touch with public opinion over an issue that has drawn strong backing from middle-class urban Indians.

The ruling coalition has scrambled to find a way out of the standoff as Hazare's fast, which is being closely followed by India's newspapers and news TV channels, begins to threaten his health.

But opposition parties see the issue as an opportunity to revive their own fortunes and observers say the all-party meeting is unlikely to provide a consensus on how to proceed with the proposed Lokpal (ombudsman) bill.

"Rousing support has compelled Hazare to take a stand against the government," Rajiv Pratap Rudy, spokesman of the Bharatiya Janata Party (BJP), a Hindu nationalist group that leads the opposition, said ahead of the meeting.

"The government should negotiate with him. We believe that his demands and his actions are legitimate," he told AFP.

Hazare appeared well on Tuesday when speaking to crowds at his fast, which is being held at a muddy open-air venue in Delhi, but his supporters said he had lost 5.6 kilogrammes (12.3 pounds) in weight.

He is attended by a team of doctors, who can be seen regularly checking his blood pressure and monitoring other vital signs.

Hazare has vowed to continue his fast unless parliament passes his version of the anti-graft bill by August 30.