What to know about the Sikh movement at the centre of the tensions between India and Canada

Tensions between Canada and India have reached new heights with dueling diplomatic expulsions and an allegation of Indian government involvement in the killing of a Sikh activist on Canadian soil.

Tensions between Canada and India have reached new heights with dueling diplomatic expulsions and an allegation of Indian government involvement in the killing of a Sikh activist on Canadian soil.

The row centers around the Sikh independence, or Khalistan, movement. India has repeatedly accused Canada of supporting the movement, which is banned in India but has support among the Sikh diaspora.

On Monday, Canadian Prime Minister Justin Trudeau in Parliament described what he called credible allegations that India was connected to the assassination of Hardeep Singh Nijjar in June. The Indian government denied any hand in Nijjar's killing while also saying Canada was trying to shift the focus from Khalistan activists there.

Here are some details about the issue:

India's Sikh independence movement eventually became a bloody armed insurgency that shook India in the 1970s and 1980s. It was centered in northern Punjab state, where Sikhs are the majority, though they make up about 1.7% of India's population.

The insurgency lasted more than a decade and was suppressed by an Indian government crackdown in which thousands of people were killed, including prominent Sikh leaders.

Hundreds of Sikh youths were also killed during police operations, many in detention or during staged gunfights, according to rights groups.