The United States is waiting to see the results of the Indian investigations on allegations related to a plot to assassinate Sikh separatist leader Gurpatwant Singh Pannun in the US, a State Department official has said.

"They (Indian government) opened a committee of inquiry to look into the matter, and that work is ongoing; we'll wait to see the results. But we made it very clear that it's something that we are taking seriously and we think they, too, should take this seriously," State Department Spokesperson Matthew Miller told reporters at his daily news conference on Monday.

Miller was responding to a question on the allegations that Indian government officials were involved in a plot to assassinate Pannun, a US citizen and a separatist Sikh leader.

"I would refer you to the Canadian authorities to speak to the details of the investigation there. With respect to the indictment that was returned in the United States, I will let the Department of Justice speak on behalf of that in detail," he told reporters.

"And then the only thing further I would say: when it comes to the State Department, we had made it clear right when these allegations were first made public that it's something we think India should take very seriously and investigate," Miller added.

The Washington Post, citing unnamed sources, recently named a Research and Analysis Wing (RAW) officer in connection with the alleged plot to kill Pannun on American soil last year.

Slamming the report by the US daily, India has strongly rejected the claims, saying that the report made "unwarranted and unsubstantiated" imputations on a serious matter and that an investigation into the case was underway.

"The report in question makes unwarranted and unsubstantiated imputations on a serious matter," External Affairs Ministry Spokesperson Randhir Jaiswal said in New Delhi last Tuesday.

Jaiswal said a high-level inquiry committee set up by New Delhi to look into inputs provided by the US on the alleged plot was still probing the case.