New York, Oct 21 (IANS) A US group that has filed a case against Indian Prime Minister Narendra Modi for alleged crimes against humanity has said it would contest the Obama administration's "suggestion of immunity" for the Indian leader.

American Justice Centre, which filed the case against Modi during his recent visit to the US, said even as sitting head of government Modi can't escape prosecution for actions prior to assuming the Prime Minister's office.

In fact, such precedence already exists in the case of former prime minister Manmohan Singh, who was also sued by the US based human rights groups for his alleged complicity in mass violence against Sikhs, it said.

On August 20, US District Judge James Boasberg had ruled that Manmohan Singh's immunity as head of state did not cover his tenure as finance minister prior to becoming the Prime Minister, AJC said.

"We will challenge the suggestion of immunity by the US Government," said Gurpatwant Singh Pannun, attorney for the AJC.

Earlier, New York's Indian American attorney Preet Bharara told a New York court that the Executive Branch had determined that "Modi, as the sitting head of a foreign government, enjoys head of State immunity from the jurisdiction of US courts."

In papers filed with the US District Court in Manhattan Sunday Bharara's office said "Modi is entitled to immunity from the jurisdiction of this court over this suit."

However, Bharara also left it open to interpretation if Modi could face charges in the US once he leaves office of the prime minister.

Bharara said under the customary international law principles accepted by the Executive Branch, head of state immunity attaches to a head of state's or head of government's status as the current holder of office.

"After a head of state or head of government leaves office, however, that individual generally retains residual immunity only for acts taken in an official capacity while in that position," he said.