A diplomatic row that has strained bilateral relations between India and Canada for over a year has boiled over as the countries expelled each other’s top diplomats over the killing of a Sikh activist in Canada and allegations of other crimes there.

The U.S. and British governments in the last 24 hours have urged India to fully cooperate with ongoing investigations by Canadian authorities alleging Indian government officials had committed "serious" crimes in Canada.

India’s government is considering the risk that senior officials could face court charges if a diplomatic fallout with Canada worsens, Indian officials familiar with the matter said. The two countries expelled each others’ envoys on Monday ...