"It is vitally important that Iran be called to account for its deplorable human rights record, including egregious violations of religious freedom," the US Commission on International Religious Freedom (USCIRF) wrote in a letter to Clinton.
"The United States must signal during the current talks its unwavering support for Human Rights for all Iranians and insist that Iran honor its international obligations on religious freedom," read the letter.
The bipartisan federal agency USCIRF was established in 1998 and monitors global religious freedom to offer independent policy recommendations to senior US officials, including the president and Congress.
The issue of human rights in Iran was raised by a US envoy on 1 October in Geneva, on the sidelines of talks regarding Iran's nuclear program.
According to the USCIRF, Iran's "systematic repression extends beyond the Shi'a majority to target religious minorities, particularly Baha'is, as well as Sufi Muslims, Jews, and Evangelical Christians."
Over the past year Iran "has intensified its targeting of these groups while increasing its anti-Semitic, Holocaust-denying rhetoric."
The Iranian government has also "taken steps toward passing a revised penal code that, in clear violation of Iran?s international legal obligations, would codify draconian punishments, including the death penalty, on converts from Islam," the group said.
The USCIRF noted that none of the US sanctions against Iran are linked to religious repression, and the group urged Clinton to prevent any Iranian "engaged in particularly severe religious freedom violations" from entering the United States, and to freeze their assets.
