WASHINGTON — President Obama is pressing United Nations nuclear inspectors to release classified intelligence information showing that Iran is designing and experimenting with nuclear weapons technology. The president’s push is part of a larger American effort to further isolate and increase pressure on Iran after accusing it of a plot to assassinate Saudi Arabia’s ambassador to the United States.
If the United Nations’ watchdog group agrees to publicize the evidence, including new data from recent months, it would almost certainly revive a debate that has been dormant during the Arab Spring about how aggressively the United States and its allies, including Israel, should move to halt Iran’s suspected weapons program.
Over the longer term, several senior Obama administration officials said in interviews, they are mulling a ban on financial transactions with Iran’s central bank — a move that has been opposed by China and other Asian nations. Also being considered is an expansion of the ban on the purchase of petroleum products sold by companies controlled by the country’s elite military force, the Islamic Revolutionary Guards Corps.
The Revolutionary Guards are also believed to oversee the military side of the nuclear program, and they are the parent of the Quds Force, which Washington has accused of directing the assassination plot.
The proposed sanctions come as administration officials confront skepticism around the world about their allegations that Iran was behind the plot and limited options about what they can do — as well as growing pressure from Republicans and some Democrats in Congress to take tougher action against Iran, with the central bank and the oil industry high on lawmakers’ lists.
All of the proposed sanctions carry with them considerable political and economic risks. Yukiya Amano, the cautious director general of the United Nations group, the International Atomic Energy Agency, talked publicly in September about publishing some of the most delicate data suggesting Iran worked on nuclear triggers and warheads. But officials who have spoken with him say he is concerned that his inspectors could be ejected from Iran, shutting the best, though narrow, window into its nuclear activities.
Similarly, China and Russia, among other major Iranian trading partners, have resisted further oil and financial sanctions, saying the goal of isolating Iran is a poor strategy. Even inside the Obama administration, some officials say they fear any crackdown on Iranian oil exports could drive up oil prices when the United States and European economies are weak. As one senior official put it, “You don’t want to tip the U.S. into a downturn just to punish the Iranians.”
Senior administration officials, who would not speak publicly about internal negotiations over the sanctions, say no recommendation on acting against the central bank has gone to Mr. Obama, who vowed last week to make sure Iran would face the “toughest sanctions” for what he said was its role in the sensational scheme to hire a Mexican drug cartel to kill the Saudi envoy.
The decision to press the International Atomic Energy Agency was brewing even before the plot against the Saudi ambassador was discovered, but that discovery prompted the White House to pursue a full-court, public press of the agency to release the sensitive intelligence.
Officials familiar with the evidence say it creates extraordinarily uncomfortable questions for the Iranians to answer, but does not definitively point to the construction of a weapon. Instead, it details work on individual technologies essential for designing and detonating a nuclear device, including how to turn uranium into bomb fuel, how to cast conventional explosives in a shape that can set off a nuclear blast, and how to make detonators, generate neutrons to spur a chain reaction, measure detonation waves and make nose cones for missiles.
Tommy Vietor, the spokesman for the National Security Council, said Saturday that “the United States believes that a comprehensive assessment would be invaluable for the international community in its consideration of Iran’s nuclear program and what to do about it.” Iran has declared that all of the documents suggesting work on how to create a weapon that could fit atop an Iranian missile are “fabrications” intended to justify an attack. The country has been the target of covert attacks, including the assassinations of some nuclear scientists and a computer worm that disabled some of Iran’s nuclear centrifuges.
The Obama administration, since coming to office, has never publicly presented detailed evidence to back up its claim that Iran is driving toward a weapon or creating the technology to assemble one quickly, should it need it. But it has discussed the evidence widely with allies.
In part the administration has hesitated to discuss the evidence because, after the failure to find weapons of mass destruction in Iraq in 2003, any American evidence is considered suspect. Widespread questions about the plot against the Saudis last week underscored how deep those suspicions run.
But Iran is a different kind of case. Inspectors visit regularly, measuring Iran’s output of uranium, including recent production of the material, enriched to 20 percent purity, that takes it far closer to the kind of fuel needed for a weapon. Iran said recently that it would produce more of the 20 percent enriched material than it needs for a small medical research reactor, which prompted new concerns that it is building a stockpile that could be converted to weapons use.
“They sought to hide their enrichment activity for years, and their covert facility at Qum, which the president revealed in 2009,” a top adviser to Mr. Obama, who spoke on the condition of anonymity because of the delicacy of the topic, said Friday. “They continue to enrich at 20 percent, and the rationale for doing so is demonstrably false.”
In June, the Treasury Department imposed sanctions on Tidewater Middle East, a company linked to the Revolutionary Guards that operates strategic container ports through which the Guards and the Quds Force have moved weapons, administration officials said. Last week, the Treasury levied sanctions on an Iranian carrier, Mahan Air, which officials said ferried weapons for the Quds Force.
A Treasury ban on transactions with the Central Bank of Iran would be powerful because any third country that did business with the central bank would be cut off from the American financial system.
“We are looking very actively at the possibility of designating the central bank of Iran, as well as taking other actions in response to this plot,” David S. Cohen, the under secretary of the Treasury for terrorism and financial intelligence, told the Senate Banking Committee. “We’re looking quite intensively at how to ratchet up the pressure.”
The administration is also weighing whether to designate elements of the Revolutionary Guards that control Iran’s oil exports, effectively banning purchases of fuel from Iran. Another option would be to require companies that sell refined fuel to the United States to certify that the fuel contains no Iranian crude oil.
But American allies like Japan and South Korea buy large amounts of oil from Iran, paying their bills through the central bank since most Iranian commercial banks are off-limits. China relies less on the central bank for its purchases but is also a large buyer of Iranian oil.
Cutting off Iran’s oil exports would have unpredictable effects on prices, officials said, with even a brief shock posing an economic threat. Iran would find new customers and would probably try to sell fuel to middlemen, who would resell it. But, officials said, the real impact was unknown.

A version of this article appeared in print on October 16, 2011, on page A1 of the New York edition with the headline: To Isolate Iran, U.S. Presses Inspectors on Nuclear Data.