Diplomats say Iran and six world powers are considering meeting again after their present talks on Iran's nuclear program and other issues end.

The diplomats say the two sides are discussing a follow-up meeting in the closing minutes of Thursday's talks during which the big-powers attempted to persuade Tehran to freeze a program that could create nuclear weapons.

A decision to meet again would be significant. The last such seven-nation talks before Thursday's gathering occurred more than a year ago and ended in failure.

The diplomats demanded anonymity for reporting on the closed meeting in Genthold, Switzerland.

Representatives from the U.S. and Iran also had significant talks on Tehran's nuclear program in a rare one-on-one meeting Thursday.

William Burns, U.S. undersecretary of state, and Saeed Jalili, Iran's top nuclear negotiator, held the bilateral discussion in a sign of President Obama's commitment to engage the Islamic Republic directly on nuclear and other issues, a sharp break with the previous Bush administration.

Diplomats and officials disclosed no details of the meeting but said ahead of the Geneva negotiations that such an encounter was possible, if Burns decided it would move along U.S. objectives.

The last time the U.S. attended the so-called P5 +1 talks -- which includes the permanent members of the U.N. Security Council and Germany -- it did so merely as an observer. 

The clear objective of Thursday's meeting was to persuade Tehran to provide full access to its nuclear program. The meeting is seen as a critical chance for Iran to either shift course or further alienate the international community. 

However, senior administration officials said the U.S. would not push for sanctions against Iran at the Geneva talks. 

The officials also said that while gaining access to inspect Iran's uranium enrichment facility near Qom is "critically important," the U.S. won't walk away from negotiations if Iran refuses.

"Tomorrow is the negotiations track and that is the thrust," a senior official said ahead of the talks. "The thrust is dealing with this nuclear program and trying to get a process underway to address the growing international concern. These will not be easy talks." 

The talks were expected to last the full day. 

Three senior officials intimately involved in the Iranian nuclear issue briefed reporters at the White House. Significantly, they avoided the term "sanctions" in describing the administration approach to talks with Iran, preferring the term "pressure track." 

"Just as you prepare the ground for negotiations, which we have done, you also prepare the ground in case this doesn't work out. We've done a lot of preparing the ground so that we would be credible on the pressure track," an official said. "The first objective is to affect Iranian behavior. We want this process to succeed. If it's not going to succeed, there has to be consequences. This is a bona-fide offer to negotiate this nuclear problem, to deal with it. Having said that, we have been quite diligent about building the other side of the track as well."

While the U.S. is demanding international inspections of Iran's previously covert uranium enrichment facility near Qom, the U.S. is prepared to keep talking if Iran refuses. Iran has already said the Qom site does not violate non-proliferation rules and inspections are unnecessary.

"Access to Qom by the IAEA (International Atomic Energy Agency) is critically important," one official said. "But I'm being cautious because I don't know what's going to be put on the table from the other side. The Iranians should grant access to Qom in a timely fashion. This would be an important thing for the Iranians to do." 

More broadly, officials said Iran needs to take "practical steps" and "produce measurable results," and needs to do so "at a pace that makes sense" for nuclear talks to continue. "The pace, the tempo of the negotiations is a critical part of this." 

As for a timeline, one official said Iran must prove its willingness to negotiate in a matter of weeks. 

The officials said Iran faces a "very, very stark choice" to either abandon its pursuit of weapons-grade nuclear material or face "isolation, pressure, sanctions and other steps." 

The U.S. has begun to draw up what officials described as "six to eight categories" of potential sanctions designed to affect Iran in "a material way." 

The officials would not specify the type of sanctions that are being considered or say if nations like Russia had dropped long-standing objections to sanctions that would hit businesses in Iran unrelated to nuclear proliferation activities. The officials were similarly mum on whether other nations, namely China, had dropped objections to sanctions on refined petroleum products. China is a major gasoline supplier to Iran through various non-official mechanisms. 

"I don't think we should go into details on what we've discussed with various nations," an official said. "The conversations take place in different ways with different countries. There's a diplomatic process underway on discussions about the pressure track." 

The officials said if Iran rebuffs what they described as a "serious, bona fide offer" to trade pursuit of weapons-grade nuclear material for enhanced trade and financial ties, the U.S. is prepared to pursue sanctions through one of three mechanisms: the United Nations Security Council; regional groups (such as the European Union); or the U.S. applying sanctions with "like-minded" nations. 

Officials said the U.S. has built a "united front" against Iran's continued pursuit of nuclear weapons, adding Iran "needs to find a way to respond because if they don't, they will pay the price for it." 

Officials said the Obama administration has been engaged since early summer in negotiations with Security Council nations and others on devising a sanctions strategy should Iran remain recalcitrant. 

The officials said Iran is facing increased international isolation due to disclosure of the Qom facility, which is not yet operational but which the U.S. regards as a clear violation of disclosure commitments. 

"The Qom announcement has brought unity and a sense of purpose to the P5+1 process," an official said. "Even sympathizers to the Iranians were sadly surprised. It has really put a lot of pressure on the Iranians." 

Senior administration officials also said blowing the cover on the Qom uranium enrichment facility has denied Iran a negotiating chip and undermined its ability to covertly produce -- once the facility came on line in roughly three months -- to produce weapons-grade nuclear material. 

"It is going to be the centerpiece of conversations," one official said, referring to access to Qom. "There's not a lot of dispute about the core facts." 

FOX News' Major Garrett and The Associated Press contributed to this report.