Vahid Salemi, File, Associated Press
FLE - In this file photo taken Monday, Sept. 22, 2014, Iranian President Hassan Rouhani briefs media prior to departing Mehrabad airport to attend the United Nations General Assembly, in Tehran, Iran. Rouhani said Sunday, Jan. 4, 2015, that ongoing nuclear negotiations with world powers are a matter of "heart," not just centrifuges ahead of talks next week in Geneva.

TEHRAN, Iran — Iranian President Hassan Rouhani said Sunday that ongoing nuclear negotiations with world powers are a matter of "heart," not just centrifuges ahead of talks next week in Geneva.

Speaking to an economic conference in Tehran, Rouhani both countered hard-line critics worried Iran will give up too much while also attempting to signal his administration remains open to negotiation with the six-nation group leading the talks.

If "we are ready to stop some types of enrichment which we do not need at this time, does it mean we have compromised our principles and cause?" Rouhani asked.

He responded: "Our cause is not linked to a centrifuge. It is connected to our heart and to our willpower."

On Jan. 15, Iranian negotiators will meet in Geneva with officials from the U.S., Russia, China, Britain, France and Germany, hoping to hammer details out of a final deal. Iran reached an interim, one-year deal with world powers in November 2013 to freeze its nuclear program in exchange for the easing of some sanctions. Negotiators later agreed to extend talks until June 30, with hopes of reaching a rough deal in March.

The West fears Iran's nuclear program could allow it to build nuclear weapons. Iran says its nuclear program is only for peaceful purposes, like power generation and medical research.

The main conflict is over uranium enrichment, which can create both reactor fuel and the fissile core of nuclear arms. In seeking to reduce Iran's bomb-making ability, the U.S. has proposed that Tehran export much of its stockpile of enriched uranium — something the Islamic Republic has long said it would not do. Two other unresolved issues are Iran's Fordo underground enrichment site and the nearly built Arak nuclear reactor.

Two diplomats in recent days told The Associated Press that Iran and the U.S. tentatively agreed on a formula about shipping its stockpile to Russia, as well as drew up a catalog outlining areas of potential accord and differing approaches to remaining disputes. On Saturday, Iranian Foreign Ministry spokeswoman Marzieh Afkham denied any tentative formula or catalog had been made.