The United States is increasingly worried by indications that Iran may be on the brink of developing a nuclear weapon, but the latest report on its atomic program from a U.N. watchdog is unlikely to sway the Obama administration from its plan to rely on sanctions and diplomatic pressure, not military threats, to deter Iranian ambitions.

Ahead of the release this week of a new report on the Iranian program from the International Atomic Energy Agency, U.S. officials said Monday the administration will use the report as leverage in making its case to other countries that sanctions against Iran should be expanded and tightened and that the enforcement of current sanctions be toughened.

The officials said the option of using force, a topic of intense speculation in Israel, Europe and the United States in recent days, to prevent Iran from acquiring an atomic weapon will not be taken off the table. Iran denies it is seeking nuclear weapons.

The possibility of a U.S. strike is considered remote, however. That is partly because there is no certainty it would successfully stop Iran and partly because of the diplomatic and political repercussions for a cash-strapped nation emerging from two wars.

Iran rebuffed President Barack Obama's early attempts at a political rapprochement, and the diplomatic distance between the two nations has appeared to widen. Iran's response to a military strike on its known nuclear facilities is a matter of speculation, but U.S. military officials have assumed Iran could retaliate with attacks on Israel or other U.S. allies within easy reach, such as Turkey. Iran could also encourage violence against U.S. interests by proxy militias such as Hezbollah.

The White House and State Department declined to comment on specifics of the report, expected to be presented on Wednesday at IAEA headquarters in Vienna, but elements have been leaking out since The Associated Press first reported details on Friday.

The report will suggest Iran made computer models of a nuclear warhead and includes satellite imagery of what the IAEA believes is a large steel container used for nuclear arms-related high explosives tests, diplomats told the AP.

One senior U.S. official familiar with the as-yet unreleased document called it "pretty compelling" and predicted it would stiffen the resolve of U.S. allies, particularly in Europe, to step up pressure on Iran to prove that its nuclear program is peaceful as it claims.

The official, who like several others spoke on condition of anonymity due to the sensitivity of the matter, said the administration is "deeply troubled" by the findings and that others should be as well. Another official said the administration would use the report to concentrate on steps designed to further isolate Iran.

White House spokesman Jay Carney said the administration expects the report "to echo and reinforce what we've been saying about Iran's behavior and its failure to live up to its international obligations and ... echo our concern about Iran's nuclear program."

Carney said the U.S. continues to focus on using diplomatic channels to pressure Iran to abandon its nuclear program. But he added that the U.S. also will keep all options open. "We, of course, never remove from the table any option in a situation like this, but we are very focused on diplomacy," he said.

The U.S. has already slapped sanctions on dozens of Iranian government agencies, financial and shipping companies as well as officials over the nuclear program and could target additional institutions like Iran's Central Bank. It has also pushed the U.N. Security Council, which has already imposed four rounds of international sanctions on Iran, for increased penalties.

But in light of Iran's continued defiance, along with intelligence suggesting the country is continuing to try to develop nuclear weapons, some, including many in Israel, have argued that military action is the only solution. Speculation has run high in Israel over the past week that the Israeli government is contemplating a strike.

The U.S., however, has urged caution.

"We've made it clear that the dual-track approach is what we favor ... engagement and international pressure. And that's where the focus of the United States government and this department has been," Defense Department spokesman Capt. John Kirby said Monday.

Pentagon press secretary George Little said the U.S. is mindful of Israel's concerns over the Iranian nuclear program and that it's been the subject of regular U.S.-Israeli discussions including during Israeli Defense Minister Ehud Barak's visit here and Defense Secretary Leon Panetta's recent trip there.

"The secretary believes he has a very strong relationship with Israeli counterparts and that the channels of communication are open," Little said. "And it would always, of course, be preferable on matters as grave as this to work closely with the Israelis if prospective action is contemplated."

Israel considers Iran to be its most dangerous enemy and the only regional power that poses an existential threat to it.

A string of Israeli leaders have repeatedly said they prefer that economic sanctions deter the Iranians from developing nuclear weapons, but have also steadfastly refused to take a military option off the table. In recent days there has been a spate of Israeli media reports on a possible strike, accompanied by veiled threats from top politicians.

An Israeli government official, who spoke on condition of anonymity because he was discussing sensitive internal deliberations, told the AP that the option is now being debated at the highest levels and that Prime Minister Benjamin Netanyahu and defense minister Barak favor military action. But the country's security chiefs oppose the operation.

In Iran, a powerful conservative cleric warned the IAEA not to sully the nuclear watchdog agency's reputation by releasing false or forged documents about Iran's nuclear program.

Ayatollah Ahmad Khatami did not address the latest IAEA progress report in detail but ridiculed Obama's Mideast policies.

"This year marked the darkest year for the inexperienced U.S. President Barack Obama in the history of the U.S. due to the collapse of the country's 'blind puppets'," such as Egyptian President Hosni Mubarak, Iran's IRNA news service reported Monday.


Associated Press writers Julie Pace and Pauline Jelinek in Washington, Edith M. Lederer at the United Nations and Aron Heller in Jerusalem contributed to this report.