GENEVA, Switzerland (CNN) -- Two "senior officials" from the United States and Iran "had a meeting on the margins" of the Geneva talks on Iran's nuclear program, U.S. spokesman Robert Wood told CNN on Thursday.
Wood wouldn't say who sat down on the sidelines of the discussion, but the encounter is regarded as the first face to face discussion between Iran and the United States over the nuclear issue.
William J. Burns, U.S. undersecretary of state for political affairs, is leading the U.S. delegation, and Saeed Jalili, Iran's nuclear negotiator, is representing his country at the meeting.
The Geneva talks coincide with the recent revelation that Iran was building a second uranium enrichment facility near the city of Qom.
"They certainly are historical talks," David Albright, president of the Institute for Science and International Security and a former weapons inspector, told CNN.
"For the United States and Iran to sit down finally and start to talk about the significant differences between the two countries is extremely important. and I think it's long overdue."
The group met at the Villa le Saugy.
The mood at the event's buffet-style lunch seemed to belie the stark international tensions over the Iranian nuclear issue. Iranians and the other officials dined and mingled, and some ate while seated, and others stood at tables, an official at the talks said.
Many gathered in the villa's backyard, and enjoyed a view of Lake Geneva and the Swiss Alps, the official said. Along with the U.S. and Iranian officials, many other would huddle together, quietly discussing issues in sidebar conversations, the official said.
The existence of the second uranium enrichment facility prompted President Barack Obama and the leaders of Britain and France to publicly chide the Islamic republic last week at the G-20 summit in Pittsburgh and threaten further sanctions.
Iran claims its nuclear program is intended for peaceful purposes, but many in the international community have accused the country of trying to develop a nuclear weapons capability.
The existence of the newly revealed nuclear site will be the centerpiece of talks, attended by Iran Germany, the European Union, and the five permanent members of the U.N. Security Council, the United States, Britain, France, Russia, and China.
One official said international powers wanted to know what kind of "steps" Iran is "willing to take to build confidence with the international community."
According to three senior U.S. administration officials, the United States wants IAEA nuclear monitors to have unfettered access to the facility.
The first option would be to persuade Iran to change its ways through dialogue, but if that fails, then isolation and sanctions are other options, they said.
"If it's not going to succeed, then there has to be consequences," an official said.
Pressure could also come from the U.N. Security Council, the United States or other like-minded nations.
"They will respond," one official said referring to Iran. "If not, they will pay the price."
But former U.S. President Jimmy Carter urged Washington and other nations to take a diplomatic approach in negotiations with Iran over the country's nuclear ambitions.
"I hope and pray that Iran will be induced to permit international inspectors to come in and observe their entire nuclear program, because what they're doing so far is completely illegal under the nonproliferation treaty," Cartet said in an interview with CNN on Thursday.
"They have a right to purify uranium and plutonium to use for nuclear power. If Iran is on the borderline, the constant threats that we or the Israelis are going to attack Iran is the best thing to force them to say, 'Let's defend ourselves.'
"I don't think Iran has made up their mind what to do, and I think the best thing we can do is engage them and stop making these idle threats."