The head of Iran's atomic energy agency has warned that his country's landmark nuclear deal with five world powers could be jeopardised by foot-dragging on a pledge of sanctions relief in exchange for Tehran's commitment to curb atomic activities.

Ali Akbar Salehi said on Monday that "comprehensive and expeditious removal of all sanctions" outlined in the agreement "have yet to be met," even though his country is honouring all its obligations under the historic pact.

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Salehi didn't blame particular countries in comments to the International Atomic Energy Agency's general conference. But other Iranian officials have faulted the United States for delays in lifting financial sanctions.

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Salehi said that the deal's "durability" depended on the other side's "reciprocal and full implementation".

Iran complains that international financial sanctions are not being lifted quickly enough under the agreement that stipulates a removal of these and other penalties imposed over Tehran's nuclear programme, in exchange for its agreement to curb atomic pursuits that could be used to make a bomb.

Iranian President Hassan Rouhani most recently sounded that theme last week at the United Nations General Assembly.

While US financial institutions remain under tight restrictions as part of non-nuclear related sanctions, Rouhani said other banks complain about confusing signals from the US Treasury Department that create a "lot of doubt" about the legality of doing business with Tehran.

"As one thing they [the US Treasury] tell them 'you are free to engage with Iran in banking activity'," he said. "At other times, they ... enter the arena with threats.

"They frighten the big banks," he said.

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But a senior US official said Washington is delivering on its commitments.

US Energy Secretary Ernest Moniz said that if Iran was disappointed in the pace of sanctions-lifting, it was because of 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 UN nuclear meeting.

"But the international banking system, international business enterprises, are going 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."

Moniz said the US 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".

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Source: Associated Press