At exactly 7.30am, two short blasts on a whistle pierced the tranquillity of the Delhi park and 40 men in white shirts, khaki shorts and black caps stood to attention before the saffron flag of the Indian Hindu nationalist movement.

First came 15 minutes of drills. Then they marched through the capital, carrying bamboo sticks and chanting to the beat of a drum, to mark the 83rd anniversary of the Rashtriya Swayamsevak Sangh, the movement's oldest and biggest group.

Finally, they performed a prayer ritual in front of an altar bearing marigolds, images of Hindu deities, two swords, a rifle and a pistol.

“No pictures of the weapons, please,” said Ravi Prakash, the owner of a handicraft export business, who also heads the local chapter of the RSS. It was said in the nicest possible way, yet his simple request spoke volumes about an organisation that helped millions of homeless Indians after Partition but also trained the man who killed Mahatma Gandhi.

Now the RSS and its offshoots stand accused of orchestrating a wave of violence against Christians, mainly in the eastern state of Orissa, opening a new chapter in India's long struggle with Hindu radicalism.

The RSS and its main sister groups - the Bajrang Dal and Vishwa Hindu Parishad - say that they campaign peacefully to rid India of the legacies of foreign invasions and to establish a Hindu state. Their leaders deny involvement in last month's bloodshed, which the Roman Catholic Church says left 60 Christians dead and 50,000 others homeless. “How can you say Hindus are involved?” Prakash Sharma, the Bajrang Dal chief, asked. “How can you be sure Christians are not killing each other?”

Such is the evidence against them, however, that the Government is now discussing imposing a ban on Bajrang Dal, which claims 1.5 million members, for the first time since 1992. Manmohan Singh, the Prime Minister, called the Orissa violence a “national shame” last week after criticism from the European Union and the United States. “We are a secular state. We are a multireligious, multicultural nation,” he said. The Indian National Minorities Commission has also called for a ban.

The problem is that the “Hindutva” movement is now so large (the RSS claims eight million members, the VHP 6.8 million) and so decentralised that it can easily sidestep any ban.

The RSS has been outlawed, briefly, three times - in 1948 after Gandhi's murder, in the Emergency of the 1970s and in 1992 after its supporters demolished the Babri mosque. The movement also encompasses hundreds of other organisations, including the Bharatiya Janata Party, the main national opposition party, which co-leads the Orissa state government.

The ruling Congress party, therefore, fears that outlawing one would only spark trouble from another, as well as rally support for the BJP before parliamentary elections due by May. When the Cabinet met on Wednesday to discuss the ban, it could not reach a decision and dispersed, saying that it needed more evidence.

There is no shortage of evidence in Orissa, according to victims and rights groups. Chandrika Digal, 22, whose mother is a Christian and father a Hindu, says that she was raped by up to 20 men who broke into her grandparents' hut on September 19. She said her attackers told her repeatedly that she was being raped because a Christian uncle had refused to become a Hindu. “They belonged to RSS. Here there is no difference between RSS, VHP, Bajrang Dal,” she told a nun caring for her, who translated her testimony for The Times.

John Dayal, president of the All-India Catholic Union, says that he has accounts from dozens of other victims in Orissa who have identified their attackers as Bajrang Dal members. “They wear bands around their heads, they carry [tridents] ... and wave saffron flags. They shout slogans identifying themselves as Bajrang Dal. They are the storm troopers of the RSS,” he said.

The RSS and its allies put blame for the violence on Western-funded Christian missionaries, who they say have bribed and coerced poor Hindus into converting. “They were trying to convert our Hindu religion into Christians!” one RSS activist at the Delhi parade shouted when the Orissa killings were mentioned. “They started it by taking Western money to convert poor Hindus. So our people stopped them!”

HOLY WAR

— The Rashtriya Swayamsevak Sangh (National Self-Reliance Society, or RSS) Hindu fundamentalist group holds sway over India's largest opposition party, the Bharatiya Janata Party (BJP)

— The RSS was founded in 1925 to promote Hindu nationalism; its most notorious moment came in 1948 when a former member shot and killed Mahatma Gandhi

— Marauding mobs aligned to the BJP and supported by the hardline Hindu group the VHP (Vishwa Hindu Parishad, or World Hindu Society) are alleged to have burnt Christians alive, gang-raped a nun and destroyed more than 140 churches and orphanages

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