Even as they prepare for new talks Thursday with Iran on its nuclear program, the U.S. and its allies are contemplating new and tighter sanctions on Tehran, in a clear signal of expectations that the negotiations may again end in failure.

The fact that the meeting is taking place at all offers some hope, reflecting both sides' desire to talk, despite a spike in tensions over last week's revelations by Iran that it had been secretly building a new uranium enrichment plant.

Ahead of Thursday's negotiations, the State Department stressed its hope that the session would open the door to more in-depth dialogue about ways Iran could alleviate concerns that its emerging nuclear program may be secretly developing nuclear weapons.

If Iran is willing to address the nuclear issues, then there likely will be subsequent meetings, State Department spokesman P.J. Crowley said in Washington.

"That process will take some time," Crowley said. "We're not going to make a snap judgment on Thursday. We're going to see how that meeting goes, evaluate the willingness of Iran to engage on these issues."

Crowley noted that President Barack Obama has said he intends to take a few months to assess Iran's position and consult with U.S. negotiating partners before deciding what next steps to take.

In Tehran, President Mahmoud Ahmadinejad said the talks will be a "test" of their respect for Iran's rights.

"This meeting is a test to measure the extent of sincerity and commitment of some countries to law and justice," Ahmadinejad said after a Cabinet meeting Wednesday, according to official IRNA news agency.

While the negotiations are formally between chief Iranian negotiator Saeed Jalili and the EU's Javier Solana, Solana will follow the lead of the five powers. The U.S., Britain, France, Russia and Germany are sending senior officials; Washington will be represented by William Burns, the under secretary of state for political affairs, while Russia is dispatching Sergey Ryabkov, a deputy foreign minister.

Only China, which appears most opposed to new U.N. sanctions on Tehran, is sending a relatively low-level representative to the talks, which were to be held at an undisclosed location outside Geneva.

Tehran's acknowledgment that it has kept silent on the plant — which can make both nuclear fuel and fissile warhead cores — has burdened the already heated atmosphere of the crucial negotiations to the point that expectations of what would constitute success are modest.

A U.S. government official confirmed to The Associated Press that commercial satellite images taken of the purported site near the holy city of Qom are generally accurate.

He confirmed that at least one of the buildings shown in the commercial images matches up to secret U.S. government imagery of the Iranian uranium enrichment facility that was publicly revealed Friday. He spoke on condition of anonymity because he was not authorized to release the information.

At least three private sector imagery analysts in the United States have focused on the site because it fits the description given by the U.S. government: it is about 20 miles from Qom, it is built into a mountainside and it has features consistent with a secret nuclear facility, parts of which the U.S. government says are underground.

Neither the U.S. government nor Iran has officially confirmed the location or the accuracy of the commercial imagery analysis.

At best, Thursday's talks could start lowering passions over the hidden plant, Iran's three-year defiance of the U.N. Security Council's enrichment ban and Western assertions that Tehran is a supporter of terror — and lead to another meeting later this year.

That, in turn, could be the start of a process that could not only end the threat of an Israeli or U.S. strike against Iran's nuclear facilities as a last resort. It could ultimately lead to an agreement on a limited Iranian uranium enrichment program — but under tight international control meant to banish concerns that it could be turned toward making warhead material.

Such hopes are tenuous. Since the five nations first proposed a set of political and economic concessions to Tehran for a full stop to its enrichment activities three years ago, Iran has expanded the program. It now has more than 8,000 centrifuges set up in its cavernous underground facility at Natanz, with most of them working to churn out fuel-grade enriched uranium.

With Iran spurning any discussion of cutting back, let alone freezing enrichment, the five powers also are ready to talk about other issues that Tehran holds dear in hopes of also engaging it on nuclear matters.

U.S. officials and a senior official from another participating country told The Associated Press ahead of the talks that Iran is expected to raise a broad range of global political concerns while the other participants focus on Iran's nuclear program, including last week's disclosure of the previously hidden enrichment plant.

But years of abortive attempts to coax Iran into at least talking about freezing enrichment have the U.S and its Western Security Council partners looking past Thursday's talks — and the possibility that they, too, will fail.

If so, say officials from two of the delegations represented at the Geneva talks, the U.S. and its Western allies will renew their push for a fourth set of U.N. Security Council sanctions.

The initial set of sanctions in 2006 focused on banning trade with Iran in materials, equipment, goods and technology that could contribute to Iran's uranium enrichment program. Iran says its program is intended to provide fuel for civilian power reactors, but the U.S. suspects it could be used to make nuclear weapons.

U.N. sanctions against Iran were expanded in March 2007 by banning arms exports from Iran and imposing a freeze on the financial assets of 28 individuals and entities. Sanctions were again extended in March 2008, restricting the import by Iran of dual-use technologies — those that can be used for both civilian and military purposes.

Washington, London, Paris and Berlin are keen to maintain at least outward unity with Moscow and Beijing on dealing with Iran. But the officials — who discuss confidential Iran strategy only on condition of anonymity — say the four Western countries are ready to do without Russia and China if they again block new U.N. sanctions out of economic or political considerations. They said discussions have already begun on tightening existing U.N. and European Union sanctions and enacting new ones.

"Our approach will be that if we cannot get something in the Security Council, we will not wait but will be certainly actively looking for other measures," a senior official from one of the five powers said.