The US has welcomed as "good and appropriate" India's decision to announce a high-level probe into its allegations that an Indian official was involved in a foiled plot to assassinate a Sikh separatist on American soil and said it is looking forward to seeing the results.

US federal prosecutors on Wednesday charged Indian national Nikhil Gupta with working with an Indian government employee in the foiled plot to kill Gurpatwant Singh Pannun, a Sikh extremist who is an American and Canadian citizen.

An unnamed Indian official appeared in an indictment filed by US federal prosecutors in a Manhattan court on Wednesday along with the Indian national, who the Department of Justice alleges hired someone in the US to assassinate Pannun.

India on Thursday described as a "matter of concern" the US charging the Indian national with conspiring to kill the Sikh separatist, and asserted that a high-level probe committee will investigate all aspects of the case.

"The government announced today that it was conducting an investigation, and that’s good and appropriate, and we look forward to seeing the results,” Secretary of State Antony Blinken told reporters travelling with him in Tel Aviv, Israel, on Thursday.

Blinken did not give any details about the case, calling it an ongoing legal matter.

"So you’ll understand I can’t comment on it in detail. I can say that this is something we take very seriously. A number of us have raised this directly with the Indian Government in past weeks," Blinken said.

Separately, the White House on Thursday also praised New Delhi for setting up its own investigations into the matter and said this will not have an impact on the India-US relationship.

"These allegations in this investigation, (we) take it very seriously. And we're glad to see that the Indians are too announcing their own efforts to investigate this. And we've been clear that we want to see anybody that's responsible for these alleged crimes to be held properly accountable," John Kirby, Coordinator for Strategic Communications at the National Security Council in the White House, told reporters at a news conference here.

However, this will not have an impact on the India-US relationship, he said, observing that the US unearthed this plot after the historic visit of Prime Minister Narendra Modi to the US in June.

"I want to be careful here that I don't get ahead of the Department of Justice and talk about an ongoing investigation. I would just say two things. India remains a strategic partner and we're going to continue to work to improve and strengthen that strategic partnership with India. At the same time, we take this very seriously," Kirby said in response to a question.

Except for the headline, this story has not been edited by The Telegraph Online staff and has been published from a syndicated feed.