The US has consistently pressed India for updates on the Indian investigation into the alleged foiled plot to kill Sikh separatist Gurpatwant Singh Pannun and made it clear that it seeks accountability in the case, a senior Biden administration official said on Wednesday.

US Deputy Secretary of State Kurt Campbell said the US raised the issue directly at the most senior levels of the Indian government.

Campbell made the comments at a virtual media briefing on his and US National Security Advisor Jake Sullivan's visit to India last week.

"We have had constructive dialogue with India on this topic and I would say that they have been responsive to our concerns," he said.

"We've made clear that we seek accountability from the Government of India and we have consistently asked for updates on the Indian committee of inquiry's investigations," the senior official said.

"And I would just simply say that we raised this issue directly with the Indian government...at the most senior levels between our two sides," he said.

Campbell was responding to a question on whether the 'murder-for-hire' plot targeting Pannun was raised during meetings that he and Sullivan held with their Indian counterparts.

In November last year, US federal prosecutors charged Indian national Nikhil Gupta of working with an Indian government employee in the foiled plot to kill Pannun in New York.

Pannun, wanted in India on terror charges, holds dual citizenship of the US and Canada.

Gupta, who was arrested in the Czech Republic in June last year, was extradited to the US on June 14.

Following the allegations by the US, India appointed a high-level inquiry committee to look into the inputs provided by the US on the plot.

In April, The Washington Post named an Indian official for allegedly plotting to assassinate Pannun on American soil.

Asked about reports suggesting that the plot was the work of some rogue elements, Campbell did not give a direct reply but said further information in the case is likely to come through law enforcement channels.

"I don't really have anything further to add to what I already said. I will say that we also believe that Indian colleagues are looking carefully at what potential institutional reforms might be necessary," he said.

"In the wake of some of these allegations and reports that you described, so look those discussions continue between the United States and India and I think anything further is likely to come through law enforcement channels," US Deputy Secretary of State said.

Following Gupta's extradition, US Attorney General Merrick Garland said it "makes clear that the Justice Department will not tolerate attempts to silence or harm American citizens." "Nikhil Gupta will now face justice in an American courtroom for his involvement in an alleged plot, directed by an employee of the Indian government, to target and assassinate a US citizen for his support of the Sikh separatist movement in India," he said.

An indictment filed by US prosecutors in a federal court in New York alleged that an Indian government employee, identified as "CC-1" directed Gupta to arrange the assassination of Pannun.

The prosecutors allege that Gupta hired a hitman to kill Pannun and paid USD 15,000 in advance.

Gupta, through his attorney, has denied the charges and said that he has been "unfairly charged".