A simmering diplomatic row that has strained bilateral relations between India and Canada has resurfaced as the countries have expelled each other’s top diplomats over a year-long dispute about the killing of a Sikh activist in Canada.

In 1974, India shocked the world by detonating a nuclear device, drawing outrage from Canada, which accused India of extracting plutonium from a Canadian reactor, a gift intended solely for peaceful use. Relations between the two nations cooled considerably – Canada suspended support to India’s atomic energy programme.

India's main opposition Congress party has urged Prime Minister Narendra Modi's government to take all political parties into confidence regarding worsening ties with Canada a day after the two countries said they expelled each other's diplomats.