The US Department of Justice in a May 2 submission asked the Washington federal court "to recognize Prime Minister Singh's immunity from this suit while in office" as determined by the US government.
The determination was "in consideration of the relevant principles of customary international law, and in the implementation of its foreign policy and in the conduct of its international relations," it said.
However, "The United States expresses no view on the merits of Plaintiffs' claims against Prime Minister Singh", the submission added.
Challenging the submission, SFJ Monday asked the court to take a "judicial notice" of the fact that Manmohan Singh is no longer the Prime Minister of India and therefore does not enjoy immunity as "head of a foreign government".
The Foreign Sovereign Immunity Act (FSIA)also does not cover acts committed by the foreign officials in their "official capacity," it said.
In April, deputy principal legal advisor of the US State Department had asked the Department of Justice to submit "Suggestion of Immunity" to the court and take necessary steps for dismissal of case against Manmohan Singh.
A Federal Court in Washington had issued summons to Manmohan Singh on charges of "funding several counter insurgency operations in state of Punjab during the 1990s resulting in more than hundred thousand Sikhs being killed extra- judicially by the security forces".
The case against Manmohan Singh was filed during his September 2013 visit under the Alien Tort Claims Act (ATCA) and Torture Victim Protection Act (TVPA).