Demonstrators march to the United Nations in a show of solidarity with Iranian people whose human rights are reportedly being abused on July 25, 2009 in New York City.

National Security Advisor Susan Rice said that Iran should allow a visit by the UN rapporteur for human rights in the country and said Washington would continue to call for freedom of expression.

She accused Iran, along with North Korea, another state locked in a nuclear showdown with Washington, of stoking global tensions to prolong repressive domestic rule.

"In Iran, as we test the potential for a diplomatic resolution to the nuclear issue, we are mindful that another key test is whether we begin to see progress on human rights," Rice told a conference organized by the Human Rights First group.

"Our sanctions on Iran's human rights abusers will continue and so will our support for the fundamental rights of all Iranians," Rice said.

"The Iranian people deserve the same right to express themselves online and through social media as their leaders enjoy."

Washington has frequently called on the Iranian government to broaden access to social media, as some senior leaders embrace Twitter and use it to comment on events such as the international nuclear talks in Geneva.

Some opponents of US President Barack Obama have complained that the issue of human rights in Iran has not been at the center of the nuclear talks between world powers and the Islamic Republic.

The president's critics also accuse him of an insufficiently robust intervention to support anti-government demonstrations in Tehran in 2009 after disputed elections.

Initially, Obama sought to avoid the United States becoming embroiled in the protests, reasoning that he could worsen the lot of demonstrators if they were seen as clients of Washington, Iran's arch foe.

But as the crackdown intensified on supporters of election candidate Mir Hossein Mousavi, Obama toughened the US line.