U.S. reportedly thwarted assassination of Sikh separatist on American soil

'We are treating this issue with utmost seriousness,' says White House rep.

There's a surprising twist in the diplomatic tensions between Canada and India, and it involves a previously unreported event in the United States. American authorities thwarted an assassination plot against a Sikh separatist, on American soil, and they believed the Indian government was involved, a British newspaper reports.