India's external intelligence service is a feared foe in its neighborhood: Pakistan, Sri Lanka and Nepal have all accused it of political meddling and involvement with outlawed groups that have perpetrated acts of violence.

Now, Canadian Prime Minister Justin Trudeau's allegation last month that Indian government agents were involved in the June killing of Sikh separatist leader Hardeep Singh Nijjar in a Vancouver suburb has thrust Delhi's secretive Research and Analysis Wing (RAW) into the global spotlight.

India angrily denied the allegations and demanded that Canada — which expelled RAW's station chief — furnish evidence. Ottawa said it shared proof with allies, but will not release it publicly.