Brandishing bamboo sticks and chanting patriotic hymns, thousands of uniformed men parade in central India, a striking show of strength by the country's millions-strong Hindu ultranationalist group.

The Rashtriya Swayamsevak Sangh -- the National Volunteer Organisation, or RSS -- marked its 100th anniversary this month with a grand ceremony at its headquarters in Nagpur.

AFP was one of a handful of foreign media outlets granted rare access to the group, which forms the ideological and organisational backbone of Prime Minister Narendra Modi's Bharatiya Janata Party (BJP), in power since 2014.

At the parade, RSS volunteers in white shirts, brown trousers and black hats marched, boxed and stretched in time to shrill whistles and barked orders.

"Forever I bow to thee, loving Motherland! Motherland of us Hindus!" they sang, in a scene that evoked paramilitary drills of the past.

"May my life... be laid down in thy cause!"

Hindus make up around 80 percent of India's 1.4 billion people.

Founded in 1925, the RSS calls itself "the world's largest organisation", though it does not give membership figures.

At the heart of its vision is "Hindutva" -- the belief that Hindus represent not........

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