At the same time, Mr. Ross said, the Biden administration has no appetite for a new crisis. “They want the priority and focus to remain on Ukraine and Russia,” he said. “Having a war in the Mideast, where you know how it starts but you don’t know how it ends, that’s the last thing they want.”

Speaking at a news briefing on Wednesday, the State Department spokesman, Matt Miller, said that “rumors about a nuclear deal — interim or otherwise — are false or misleading.”

“Our No. 1 policy is ensuring that Iran never obtains a nuclear weapon, so of course we’ve been watching Iran’s nuclear enrichment activities,” Mr. Miller added. “We believe diplomacy is the best path to help achieve that, but we are preparing for all possible options and contingencies.”

The American denial of a pending “nuclear deal” could hinge on semantics, however, if the outcome amounts to the informal understanding described by multiple officials. Such an understanding would also avoid the need for approval from a U.S. Congress deeply hostile to Iran.

In an unexpected rhetorical shift, Iran’s supreme leader, Ayatollah Ali Khamenei, said on Wednesday that he could endorse an agreement with the West if Iran’s nuclear infrastructure was kept intact, according to state media reports. Mr. Khamenei also said that Iran should maintain at least some cooperation with international nuclear inspectors.

Israel has warned that Iran could suffer dire consequences from producing bomb-worthy uranium. “If Iran enriches to the 90 percent weaponized level, it would be a great error and the price would be heavy,” Israel’s defense minister, Yoav Gallant, said in May.

Even if Iran were to use its high-speed centrifuges to purify uranium to a level suitable for making a nuclear weapon, it would still take time to construct such a bomb. In March, the chairman of the U.S. Joint Chiefs of Staff, Gen. Mark A. Milley, told a House subcommittee that process could take “several months.”