The family of an Indian man in Czech custody, whom the U.S. accuses of involvement in an unsuccessful plot to kill a Sikh separatist on American soil, on Friday asked India's top court to direct the government to give him consular assistance.

The man, Nikhil Gupta, 52, has been accused by U.S. federal prosecutors of working with an Indian government official on the plot to kill a New York City resident who advocated for a sovereign Sikh state in northern India.

Gupta was arrested by Czech authorities in June when he travelled from India to Prague and is awaiting extradition to the U.S.

The Gupta family petition said he was "illegally detained" in Prague, denied the right to contact his family in India and the freedom to seek legal representation.

It requested the court direct the Indian government to provide Gupta with consular assistance to ensure he gets a fair extradition hearing in Prague.

The court posted the petition for hearing on Jan. 4.

India has expressed concern about one of its government officials being linked to the plot, from which it dissociated itself, and said it would carry out its own investigation.

The Indian foreign ministry spokesperson did not respond to a request for comment from Reuters on Friday.

The case is delicate for both Prime Minister Narendra Modi's government and the Biden administration as they try to build closer ties in the face of an ascendant China perceived as a threat for both democracies.

It comes two months after Canada said there were "credible" allegations linking Indian agents to the June murder of a Sikh separatist leader, Hardeep Singh Nijjar, in a Vancouver suburb, a contention India has rejected. (Editing by YP Rajesh and Christina Fincher)