"Modi shall not be granted the privilege of US visa because of the very serious doubts that remain and that hang over Modi relative to his role in the horrific events of 2002 in Gujarat," said Katrina Lantos Swett, vice chairwoman of the United States Commission on International Religious Freedom.
The bipartisan government commission reviews the facts and circumstances of religious freedom violations and makes policy recommendations to the US President, the secretary of State and Congress.
"There are many, many unanswered questions that remain, there are at are many grave allegations, there are huge doubts," she was quoted as saying by the New York Times.
When asked about the possibility of Mr Modi's nomination as the BJP's prime ministerial candidate for the next Lok Sabha polls, she said, "It is no outside nation's or no individual's role to tell them who should be the next leader of India."
"For the people of India, I think it is important for them to consider very carefully who it is who they want to be their next prime minister," she added.
In 2005, the US denied Mr Modi a diplomatic visa and revoked his existing tourist/business visa under the Immigration and Nationality Act, which makes a foreign government official who is responsible for particularly severe violations of religious freedom ineligible for an American visa, the NYT said.
"Obviously what happened in 2002 in Gujarat was sectarian violence on a really massive scale. I don't think you can say that that wasn't a religious issue. It was a religious issue and the 2005 visa denial harks back to that," she said.
Mr Modi has been lobbying hard to get the decision reversed.
During a recent visit to the US, BJP president Rajnath Singh had said he would request for a review of visa ban on Mr Modi.
When pointed out that courts have not yet found any evidence of Mr Modi's involvement in the 2002 riots, Ms Swett said: "Certainly in our system of justice you can be found not guilty, which is not the same thing as found innocent."
"Under these circumstances we should follow our laws, which say that we should not give a visa. Of course Modi wants us to reverse our position because that would be part of his rehabilitation process," she said.
"One of the things that concern us is that Modi seems more concerned with rehabilitating his own reputation than with providing recompense and rehabilitation for the surviving victims of those terrible events," she added.