An Indian national has been charged with plotting to assassinate a Sikh separatist leader on US soil, the Justice Department said on Wednesday, alleging an Indian government official was also involved in the planning.

The Justice Department unsealed murder-for-hire charges against Nikhil Gupta, 52, "in connection with his participation in a foiled plot to assassinate a US citizen" of Indian origin in New York City, it said in a statement.

The man allegedly targeted in the killing "is a vocal critic of the Indian government and leads a US-based organisation that advocates for the secession of Punjab," a northern Indian state with a large population of Sikhs.

An Indian government official, directing the plan from India, worked with Gupta and others based around the world, the US government said.

Gupta, who lives in India, was arrested by authorities in the Czech Republic under US extradition orders.

The news comes after the White House said last week it was treating an alleged plot to assassinate a Sikh separatist on American soil with the "utmost seriousness," and had raised the issue with the Indian government.

The Financial Times reported that same day that US authorities had thwarted a conspiracy to kill Gurpatwant Singh Pannun, a US and Canadian citizen.

The Justice Department, which did not identify the target of the alleged assassination attempt on Wednesday, said that Gupta was recruited into the effort in May 2023.

Canada and India had a major diplomatic row after Canadian Prime Minister Justin Trudeau in September linked New Delhi to the killing of Canadian citizen Hardeep Singh Nijjar, also a Sikh separatist, in June.

New Delhi called the Canadian allegations "absurd."

The Justice Department said that after Nijjar's killing, Gupta told undercover US officials that there was "now no need to wait" on killing the New York City target.

An Indian government spokesman on Wednesday said that the United States has "shared some inputs pertaining to nexus between organised criminals, gun runners, terrorists and others."

"We had also indicated that India takes such inputs seriously since they impinge on our national security interests," the statement said, adding that a "high-level Enquiry Committee" was established on November 18 "to look into all the relevant aspects of the matter." (AFP)