Now, with a near-total U.S. embargo in place, Iran’s economy is suffering, oil sales are down, and the pact’s other signatories, including European nations, have struggled to maintain investments in Iran.

Their country is isolated, these Iranians said, and has few options other than to mount a strong response.

“Maybe if this nuclear problem had never started, things would not have escalated to this point,” said Fahimeh, a private-sector employee in Tehran, referring to Iran’s original pursuit of nuclear energy. “But now that we are here, I can understand why [Iranian] officials have no better option than to threaten uranium enrichment.”

Farzad, the engineer, said he believes Iran’s threats to increase its enriched uranium “are more severe than the actual steps they are taking in practice.”