Canada has accused India of involvement in the killing of a separatist Sikh leader on its soil -- a charge denied by New Delhi as "absurd".
Hardeep Singh Nijjar, who was slain near Vancouver in June, was an activist campaigning for the establishment of "Khalistan", an independent Sikh homeland in India.
The Khalistan campaign dates back to India's independence and has been blamed for the assassination of a prime minister and the bombing of a passenger jet.
It has also been a sore point between India and several Western nations home to large Sikh populations, with New Delhi demanding Canada and others take stricter action against separatists.
Here is what we know about the Khalistan movement:
- What is the Khalistan movement? -
Sikhism is a minority religion originating in northern India that traces its roots back to the 15th century and drew influences from both Hinduism and Islam.
Its adherents make up less than two percent of India's 1.4 billion people but Sikhs are nearly 60 percent of the population in the northern state of Punjab, the faith's heartland.
The Indian subcontinent won independence in 1947 as it was suffering through the blood-soaked Partition that divided the former British colony along religious lines.
Muslims fled to the newly formed nation of Pakistan while Hindus and Sikhs fled to India in the ensuing violence, which killed at least one million people.
The historical region of Punjab was split between the two countries and was wracked by some of the worst violence of Partition.
Canada-based Sikh extremists were accused of carrying out the 1985 bombing of an Air India flight, killing 329 people.
Memories of the insurgency still haunt India, which has outlawed the Khalistan movement and listed several associated groups as "terrorist organisations".
Since the insurgency ended, displays of support for the Khalistan movement in Punjab are rare and have been quickly clamped down upon by authorities.
Indian police in April arrested firebrand Sikh leader Amritpal Singh, who had returned to Punjab from abroad the previous year and begun preaching for a separate Sikh homeland.
Singh was caught after leading authorities on a weekslong manhunt that saw mobile internet cut off for days in the state, home to 30 million people.
- Who supports the movement? -
The Khalistan movement's main vocal advocates are these days primarily among the large Sikh diaspora, particularly in Canada, Britain and Australia.
Fringe Sikh groups periodically hold referendums to endorse the establishment of a Sikh homeland in India.
India has often complained to foreign governments about the activities of Sikh hardliners who, it says, are trying to revive the insurgency.
Earlier this year, Indian consulates in Britain and the United States were vandalised by Khalistan supporters.
