More than $10 million a year will be needed from member states to monitor the proposed deal, said Yukiya Amano, director general of the International Atomic Energy Agency, and funds are already running out.

"The Agency has immediate funding needs related to the continuing costs of implementing monitoring and verification under the existing Joint Plan of Action. These total 800,000 euros per month," Amano said in remarks prepared for the U.N. nuclear watchdog's board of directors.

"The extra-budgetary contributions which we have previously received for this purpose will be exhausted by the end of September," he said.

A further 160,000 euros ($185,000) per month will also be needed between the day the agreement is adopted and when it's implemented, he added, as the IAEA carries out preparatory work to enable the verification and monitoring process.

After months of talks, Iran and six world powers including the United States reached a broad agreement in July in which Iran agreed to curbs on its nuclear program, including invasive inspections, in exchange for a repeal of crippling sanctions.

Under the deal, the IAEA will be responsible for determining the protocol and carrying out the inspections of Iranian nuclear sites.

Critics in the U.S. Congress, which will vote in September on whether to reject the deal, have repeatedly raised questions about how those inspections will be handled.

Amano said the IAEA was ready to undertake the additional work resulting from the agreement and has the expertise needed to do so, with what is planned representing "a very robust verification mechanism in Iran."

But, he said, member states will have to find the extra money to pay for it since it won't come from the IAEA's existing budget, which runs to the end of 2016.

"There is now a historic opportunity to resolve the Iran nuclear issue. I hope that full use will be made of this opportunity," he said.

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