Iran's top leaders have agreed to answer all remaining questions about their country's nuclear past within four weeks after talks with the U.N.'s chief nuclear inspector, his spokeswoman said Sunday.

Melissa Fleming, spokeswoman for International Atomic Energy Agency chief Mohamed ElBaradei, also said that ElBaradei was given new information on Iran's "new generation of centrifuges." That issue is a top priority for the agency as it tries to establish how far advanced Iran is in developing the technology, which could be used in a weapons program.

The four-week deadline is meant to wrap up an IAEA probe of past Iranian nuclear programs. A diplomat familiar with the talks said that investigation now was focused on the most delicate aspects of the Tehran's past atomic work, including programs linked to U.S. suspicions Tehran had conducted experiments linked to nuclear arms.

The probe was originally slated to be completed in December, and the United States and its allies have been chafing at the delay, say diplomats accredited to the IAEA. But they are unlikely to object publicly if the extension allows ElBaradei to reveal details of such secret programs.

In Abu Dhabi on Sunday, U.S. President George W. Bush said Tehran "defies the United Nations and destabilizes the region by refusing to be open and transparent about its nuclear programs and ambitions." Calling Iran the "world's leading state sponsor of terror," he urged Arab nations to join with the U.S. to confront the danger "before it's too late."

Fleming's e-mailed comments were issued just a few hours after ElBaradei's plane touched down in Vienna, ending a two-day visit to Tehran that included unprecedented meetings with both Ayatollah Ali Khamenei, Iran's supreme leader, and President Mahmoud Ahmadinejad.

The diplomat said the talks went "very well," adding that — beyond discussing the progress of his agency's probe into Iran's nuclear past — ElBaradei was able to press his case for the need for Tehran to suspend uranium enrichment, a key U.N. Security Council demand.

Separately, however, a senior diplomat expressed doubt ElBaradei was able to persuade the Iranians to freeze enrichment and noted Western efforts for additional U.N. sanctions against the Islamic republic would continue unless that condition was met. Both spoke on condition of anonymity because they were not authorized to comment publicly on the issue.

Fleming's statement appeared to jibe with the first diplomat's comments on enrichment, saying the Tehran talks included "the importance of the implementation of the Additional Protocol as well as on other confidence building measures called for by the Security Council."

The Security Council has demanded Iran suspend enrichment — which can create both nuclear fuel and the fissile core of warheads — as a "confidence building measure." It has additionally urged Tehran to restore broader inspection rights for the IAEA by reinstating the "Additional Protocol" granting agency experts such powers after suspending it more than a year ago.

Alluding to the IAEA probe of Tehran's past nuclear activities launched last year, Fleming also said that the talks resulted in agreement that the "work plan should be completed in the next four weeks."

Under the plan, Iran committed itself to answering all lingering questions about its past nuclear activities — including those it has evaded since 2003, when nearly 20 years of clandestine atomic work on the part of Tehran were revealed.

Publicly, the agency has been careful about the progress of its probe.

In an August report, ElBaradei said the agency felt that information provided by Iran on past small-scale plutonium experiments had "resolved" agency concerns about the issue. It has also confirmed that Tehran has given agency experts a copy of documents showing how to form uranium metal into the spherical shape of warheads.

But it specified that Iran still needed to satisfy the agency's curiosity about the issues that are potentially more important in determining whether the country has or had a military program — among them, the "Green Salt" project, the history and present state of its enrichment technology and the origins of traces of highly enriched uranium at a facility linked to the military.

The first diplomat said those were among the issues now under discussion. Shortly before ElBaradei's trip, diplomats had told the AP that Tehran had ended years of stonewalling and begun providing some information on the topics.

"Iran also provided information on its research and development activities on a new generation of centrifuges," said Fleming's statement.

While IAEA experts have access to Iran's declared enrichment program using outmoded P-1 centrifuges, it has been kept in the dark about the existence of the state of the art p-2 machine.

Iranian officials confirmed the existence of a P-2 research program only last year. Up to November, diplomats told the AP that agency had recently been denied access to a workshop testing and developing the P-2.

The issue is important because large-scale use of P-2s would allow Iran to accelerate its enrichment program, which Tehran insists is only to create the capability to generate electricity.