A furious diplomatic row between India and Canada has pushed an otherwise fringe separatist campaign for an independent Sikh homeland in Punjab into the international spotlight.
The "Khalistan" campaign dates back to India's 1947 independence, and has been blamed for the assassination of a prime minister and the bombing of a passenger jet.
It has been a bitter issue between India and several Western nations with large Sikh populations.
New Delhi demands stricter action against the Khalistan movement, which is banned in India, with key leaders accused of "terrorism".
Canada has alleged that India arranged the 2023 killing in Vancouver of a Khalistan campaigner, 45-year-old naturalised Canadian citizen Hardeep Singh Nijjar. Four Indian nationals have been arrested in connection with the murder.
New Delhi, who wanted Nijjar for alleged terrorism offences, calls the allegations "absurd".
In a separate case, in which New Delhi is cooperating, the United States has accused India of directing a 2023 failed assassination plot in New York.
The alleged target was another Khalistan campaigner, dual US-Canadian citizen Gurpatwant Singh Pannun.
The US State Department on Wednesday said India had told it that an intelligence operative accused of directing the plot was no longer in government service.
Sikhism originated in northern India in the 15th century, drawing influences from Hinduism and Islam.
Its adherents make up less than two percent of India's 1.4 billion people.
In Punjab however, a wealthy northern state with some 30 million people, Sikhs make up nearly 60 percent of the population.
Punjab was split in the bloody turbulence of 1947, when the former British-ruled Indian subcontinent was split along religious lines.
Muslims fled to newly-formed Pakistan. Hindus and Sikhs fled to India.
The wider Punjab region was divided by the new border, and suffered some of the worst violence.
Since then, some Sikhs have called for the creation of "Khalistan", a separate Sikh nation carved out of Punjab.
In the early 1980s, charismatic Sikh fundamentalist Jarnail Singh Bhindranwale launched a violent insurgency in the name of establishing Khalistan.
In 1984, Bhindranwale and his heavily armed supporters barricaded themselves inside the Golden Temple, the faith's holiest shrine in the city of Amritsar.
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