Iran halted its nuclear weapons development program in the fall of 2003 under international pressure, but is continuing to enrich uranium and could be capable of developing a weapon as early as late 2009, the U.S. intelligence community has concluded.

The "high confidence" conclusion was revealed in a declassified portion of a national intelligence estimate released Monday.

The new intelligence estimate "confirms that we were right to be worried about Iran seeking to develop nuclear weapons. It tells us that we have made progress in trying to ensure that this does not happen. But the intelligence also tells us that the risk of Iran acquiring a nuclear weapon remains a very serious problem," National Security Adviser Stephen Hadley said in a written statement.

Click on FOXNews.com at 3:30 p.m. EST to watch a news briefing with National Security Adviser Stephen Hadley.

The findings are a change from two years ago, when U.S. intelligence agencies believed Iran was determined to develop a nuclear capability and was continuing its weapons development program.

Click here to read the unclassified version of the new assessment on Iran's nuclear capabilities.

"Tehran's decision to halt its nuclear weapons program suggests it is less determined to develop nuclear weapons than we have been judging since 2005," states the unclassified summary of the secret report. "Our assessment that the program probably was halted primarily in response to international pressure suggests Iran may be more vulnerable to influence on the issue than we judged previously."

Officials said the findings show diplomacy is effective in containing Iran's nuclear ambitions.

"This is good news in that the U.S. policy coupled with the policies and actions of those who have been our partners appear to have had some success. Iran seems to have been pressured," one official said. "Given that good news we don't want to relax. We want to keep those pressures up."

Despite the new conclusions, the report makes clear that intelligence gaps mean a judgment can't be made on whether Tehran is willing to continue the halt of its nuclear weapons program indefinitely or has set specific deadlines or criteria to prompt the continuation of the program.

It also concludes that Iran's decision to halt the program is likely based on a cost-benefit approach, influenced by international pressure, "rather than a rush to a weapon irrespective of the political, economic, and military costs."

"In our judgment, only an Iranian political decision to abandon a nuclear weapons objective would plausibly keep Iran from eventually producing nuclear weapons — and such a decision is inherently reversible," the report states.

Principal Deputy Director of National Intelligence Donald M. Kerr said officials decided to release the unclassified conclusions because "the intelligence community is on the record publicly with numerous statements based on our 2005 assessment on Iran. Since our understanding of Iran's capabilities has changed, we felt it was important to release this information to ensure that an accurate presentation is available."

The unclassified portion of the NIE being made public is nine pages in length, five of which explain methodology. The key judgments conclude with "high confidence" that:

— Until fall 2003, Iranian military entities were working under government direction to develop nuclear weapons;

— In fall 2003, Tehran halted its nuclear weapons program;

— The halt lasted at least several years;

— Iran has the scientific, technical and industrial capacity eventually to produce nuclear weapons if it decides to do reverse course;

— The halt, and Tehran's announcement that it has suspended its declared uranium enrichment program and signed additional safeguards relating to the Nuclear Non-Proliferation Treaty are "primarily in response to increasing international scrutiny and pressure resulting from exposure of Iran's previously undeclared nuclear work"; and

— Iran will not be technically capable of producing and reprocessing enough plutonium for a weapon before about 2015.

The judgments find with "moderate-to-high confidence" that:

— Iran does not currently have a nuclear weapon;

— Tehran at a minimum is keeping open the option to develop nuclear weapons; and

— Iran has not obtained enough weapons-usable fissile material to develop nuclear weapons, though the NIE assesses with low confidence the importation at all of some material. The report does not rule out that Iran "has acquired from abroad — or will acquire in the future — a nuclear weapon or enough fissile material for a weapon."

The judgments also find with "moderate confidence" that:

— Tehran had not restarted its nuclear weapons program as of mid-2007, but the NIE notes that its intentions to develop weapons is unknown;

— The earliest possible date Iran would be technically capable of producing enough highly enriched uranium for a weapon is late 2009, but that is very unlikely;

— More likely is that it would be technically capable of producing enough highly enriched uranium for a weapon sometime between 2010 and 2015;

— Iran probably would use covert facilities rather than its declared nuclear sites in its effort to produce highly enriched uranium for a weapon.

The report concludes that Iran resumed its declared centrifuge enrichment activities in January 2006 despite the continued halt in the nuclear weapons program, and made significant progress in 2007 installing centrifuges at Natanz, its chief nuclear plant.

In those efforts, Iranian agencies are still working on creating the technology that could be used for producing nuclear weapons, if it turned toward that activity.

"Since fall 2003, Iran has been conducting research and development projects with commercial and conventional military applications — some of which would also be of limited use for nuclear weapons," the report states.