VIENNA — Indirectly warning the United States, the head of Iran’s atomic energy agency said Monday that his country’s landmark nuclear deal with could be jeopardized by foot-dragging on sanctions relief, promised in exchange for Tehran’s commitment to curb key atomic activities. But a senior U.S. official said Washington is delivering on its commitments.

Iran complains that international financial sanctions are not being lifted quickly enough under the agreement with the U.S. and five other world powers that stipulates a removal of these and other penalties imposed over Tehran’s nuclear program. Tehran in turn agreed to limit atomic pursuits that could be used to make a bomb.

Nuclear agency chief Ali Akbar Salehi did not blame particular countries in comments to the International Atomic Energy Agency’s general conference. But other Iranian officials have faulted the United States for perceived delays in lifting financial sanctions, and Salehi warned that the deal’s “durability” depended on the other side’s “reciprocal and full implementation.”

“Comprehensive and expeditious removal of all sanctions” outlined in the agreement “have yet to be met,” even though Iran is honoring all its obligations under the pact, he said.

But U.S. Energy Secretary Ernest Moniz said that if Iran was disappointed in the pace of sanctions-lifting, it was due to international caution about doing business with Tehran.

“We have carried out fully our responsibilities beyond the letter of the agreement,” he told reporters on the sidelines of the U.N. nuclear meeting.

“But the international banking system, international business enterprises, are going to have to not only have clarity on where the lines are drawn on the sanctions but they’re going to have to have more business confidence, if you like, which is going to take obviously more time than Iran would like to see.”

While U.S. financial institutions remain under tight restrictions as part of non-nuclear related sanctions, Iranian President Hassan Rouhani last week said confusing signals from the U.S. Treasury Department create a “lot of doubt” about the legality of doing business with Tehran.

“As one thing they (U.S. Treasury) tell them ‘you are free to engage with Iran in banking activity,'” he told the U.N. General Assembly. “At other times, they … enter the arena with threats.

“They frighten the big banks,” he said.

Moniz, however, said the U.S. State and Treasury departments “at their highest levels” have held briefings with European banks “where they have made very clear that these sanctions have been lifted.”