29 December 2012 Last updated at 06:08 ET 
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Sanjoy Majumder reports from a protest in Delhi
Police in India have sealed off much of the capital, Delhi, and issued an appeal for calm after the death of a woman who was gang-raped in the city.
The 23-year old woman, who has not been identified, died early on Saturday at a hospital in Singapore, where she had been taken for specialist treatment.
The attack on 16 December triggered violent public protests in India.
Six men who had been arrested in connection with the rape have now also been charged with murder.
Two police officers have already been suspended.
The woman's body is to be flown back to India for burial.
On Saturday, police sealed off large parts of central Delhi close to government buildings, closed down a number of metro railway stations and asked people not to travel into the city.
Hundreds of armed police and riot troops are on duty, many of them women, and Delhi's police commissioner Neeraj Kumar has called on the public to remain calm.
Gatherings of more than five people have been banned in the city centre.
But on Saturday morning, a few hundred people gathered at the Jantar Mantar observatory, one of the areas of the city where protests are permitted, said the BBC's Sanjoy Majumder in the city.
One protester, Poonam Kaushik, blamed the attack on "the government's inefficiency to ensure safety of women in Delhi" and said the woman's death would generate "even more anger".
One banner on display told politicians: "We don't want your condolences! We don't want your fake sentiments! We demand immediate action to strengthen the laws against sexual violence."
Delhi's Chief Minister Sheila Dikshit - who has described the death as a "shameful moment" for the country - arrived to speak to the protesters but was shouted down, says our correspondent.
Protests have also been held in other cities across the country, including Calcutta and Mumbai.
Continue reading the main story We need to repent. And repentance would not be in hanging the accused or castrating them. Repentance will be in ensuring that no-one else goes through what she had to"
End Quote There has also been an angry reaction in the Indian media, with one editorial in the Times of India calling for wider changes in society and an awareness that as well as attacks on the street, there are "a thousand unheard voices" of women who face sexual violence at home.
'Constructive action' The Mount Elizabeth hospital in Singapore said the woman "passed away peacefully" early on Saturday with her family by her side.
Hospital chief executive Kelvin Loh said she had been in "an extremely critical condition" since arriving there, and had suffered severe organ failure following serious injuries to her body and brain.
The Indian home minister said the government had decided to send the woman abroad for treatment on the recommendation of her doctors.
India's Home Affairs minister, Ratanjit Pratap Narain Singh, said he was "heartbroken" by her death.
"I can only assure the family that the government will take whatever steps are needed to ensure that her killers get the harshest punishment in the quickest of time," he said.
"The government will work overtime to try and bring about laws and steps that will ensure that no other person, no other citizen of this country, has to go through or undergo the same kind of trauma."
Indian Prime Minister Manmohan Singh said he was "very saddened" by the woman's death, and that the angry public reaction was "perfectly understandable".
"It would be a true homage to her memory if we are able to channel these emotions and energies into a constructive course of action," he said in a statement.
He called on politicians and the public to set aside "narrow sectional interest" and work together to make India "a demonstrably better and safer place for women to live in".
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India's High Commissioner to Singapore, TCA Raghavan: "We extend our condolences to the family"
The woman - a medical student - and her friend had been to see a film when they boarded the bus in the Munirka area of Delhi, intending to travel to Dwarka in the south-west of the city.
Police said she was raped for nearly an hour, and both she and her companion were beaten with iron bars, then thrown out of the moving bus into the street.
The assault sparked angry protests about the general conditions for women in India, and about what is seen as an inadequate police response to rape allegations.
Officials have since announced a series of measures intended to make Delhi safer for women.
These include more police night patrols, checks on bus drivers and their assistants, and the banning of buses with tinted windows or curtains.
The government has also said that it will post the photos, names and addresses of convicted rapists on official websites to shame them.
It has set up two committees - one looking into speeding up trials of cases involving sexual assaults on women, and the other to examine the lapses that might have led to the incident in Delhi.
But the protesters say the government's pledge to seek life sentences for the attackers is not enough - many are calling for the death penalty.
