The US last week penalised a number of Iranian and foreign companies for violating sanctions against Tehran.
Western officials have long said Iran must address the UN agency's suspicions about its work.
All sides agreed to continue talking for four more months to try reach a final agreement.
Six world powers are negotiating with Iran to scale back on enrichment capacity sharply.
Israel has warned it could bomb nuclear sites if it deems diplomacy incapable of reining in Tehran.
The EU-coordinated talks stumbled during the last round of negotiations in mid-May.