Indian Prime Minister Narendra Modi is focussed on combating Sikh separatism, despite its scant support among the country's small religious minority, due to security and political concerns, officials and experts say.

The movement for a Sikh homeland in northern India, crushed decades ago, has burst onto the global stage in recent months as the United States and Canada accused Indian officials of involvement in assassination plots against Sikh separatist leaders in North America.

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New Delhi denies any connection to a June murder in a Vancouver suburb but has announced an investigation into U.S. concerns about an alleged plot in New York. It says such plots were not government policy and it is not hunting down Sikh separatists abroad.

The diplomatic dust-ups with normally friendly Washington and Ottawa highlight the outsized role Sikh separatism plays in the political calculus of Modi's Hindu-nationalist government, which is in a strong position to win national elections next year.

Indian security officials say they must crack down on what they call Sikh connections to crime overseas linked to the Sikh heartland of Punjab. Sikh nationalists reject that claim, saying Modi is trying to destroy their leadership and mobilise his Hindu base.

Other Modi critics say he is exploiting the issue for political gain after Sikh farmers dealt his government one of its biggest blows by forcing a rollback of agricultural reforms.