DUBAI, United Arab Emirates — American and European officials said Friday that a mission by international nuclear inspectors to Tehran this week had failed to address their key concerns, indicating that Iran’s leaders believe they can resist pressure to open up the nation’s nuclear program.

The assessment came as Iran’s supreme leader lashed out at the United States, vowing to retaliate against oil sanctions and threats of military action and warning that any attack “would be 10 times worse for the interests of the United States” than it would be for Iran.

While the inspectors from the International Atomic Energy Agency, who returned to Vienna after a three-day mission in Tehran, said nothing substantive about their trip and were planning to return to Iran later this month, diplomats briefed on the trip said that Iranian officials had not answered the questions raised in an incriminating report issued by the agency in November.

That report cited documents and evidence of experiments with detonators that strongly suggested Iran might have worked on technologies to turn its nuclear fuel into working weapons and warheads. Tehran has insisted its uranium enrichment activities are peaceful and has dismissed the evidence suggesting otherwise as fabricated or taken out of context, and has refused to engage in substantive discussions or inspections.