The Indian Army has been shocked by the arrest of a senior Military Intelligence officer on suspicion of involvement in a bomb attack by Hindu extremists in western India in September.

Colonel Srikant Prasad Purohit is the first serving officer in India's Army — seen as a bastion of secularism since the country's independence in 1947 — to be arrested on terrorism charges.

His detention is prompting calls for a ban on Hindu nationalist groups accused of stirring political violence, including recent attacks on Christians in eastern India, before national elections next year.

It may also force Indian authorities to investigate whether Hindu radicals were behind other recent bomb attacks, many of which have been blamed on Islamic extremists backed by Pakistan's intelligence service.

Colonel Purohit, 37, was arrested in Bombay on Wednesday on suspicion of involvement in a bomb attack that killed at least six people near a mosque in the western city of Malegaon on September 29.

The Anti-Terror Squad (ATS) of the surrounding state of Maharashtra is now questioning him at its headquarters in Bombay, according to Dinesh Agarwal, an ATS spokesman.

Inspector Agarwal denied Indian media reports that Colonel Purohit had confessed to masterminding the explosions, and that the ATS wanted to question other serving military officers.

"The investigation is progressing," he told The Times. "Questioning other serving officers is not on the cards now."

However, he confirmed that the ATS had arrested eight other civilians, including a retired army major, Ramesh Upadhyay, on suspicion of involvement.

Investigators say that Colonel Purohit and Major Upadhyay were both members of Abhinav Bharat (New India), a Hindu nationalist organisation founded in the western city of Pune in June 2006.

Abhinav Bharat's President is Himani Savarkar, the niece of the Hindu radical who assassinated Mahatma Gandhi, the Indian independence leader, in 1948.

She accuses India's ruling coalition — led by the Congress Party — of trying to smear Hindu nationalists and has offered legal aid to all the arrested members of Abhinav Bharat.

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