Vienna: Rafael Grossi, the head of the UN's nuclear watchdog, acknowledged on Monday that Iran's concessions to him during his visit to Tehran over the weekend will largely depend on future negotiations. He also took back some remarks he had made after his return.

The International Atomic Energy Agency (IAEA) and Iran announced they had reached an agreement to advance a number of issues, including a long-stalled IAEA investigation into uranium particles discovered at three unreported sites in Iran, two days before a quarterly meeting of the IAEA's 35-nation Board of Governors.

Grossi stated at a press conference on Saturday that they had agreed to re-install all additional monitoring tools, such as security cameras, at nuclear sites that had been installed as part of Iran's 2015 nuclear agreement with major powers but had been taken down last year as part of the deal's implementation.

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At a news conference on Monday, Grossi acknowledged that future technical discussions would have a significant impact on this and other issues. "We will have to discuss...this, how do we do it," he said.

"We have our own opinions, and this will be covered in the technical discussions that will be held in the wake of my visit and the joint statement. And to do that, a technical team will be going to Iran very soon," he added.

An effort by the West to pass another resolution similar to the one that was passed at the most recent quarterly board meeting ordering Iran to cooperate with the uranium investigation appears to have been defeated by the announcement of apparent progress in a joint statement released on Saturday that provided few details.

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The Islamic Republic typically rebels against such resolutions and has previously retaliated by stepping up the nuclear activities that the 2015 agreement was intended to curtail.

"Why don't you allow us to do what we do? Unless you want to come work with us as an inspector, which might be fun. When asked how much Iran had firmly committed to and how much depended on future negotiations, Grossi responded, "We know how to do these things.

"I think this is a great opportunity. Of course, I cannot promise. When people claim that these were (only) promises, let's start by saying that they aren't. There are some concrete agreements that we do have. I must do my job and never give up at the same time.

At this week's board meeting, the United States said only that Washington was in discussions with European allies and the IAEA on "the most effective means" to get Iran to keep its commitments but gave no indication of how sternly it might push Iran to comply.

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Ned Price, a spokesman for the US State Department, told reporters at a regular briefing, "Iran must cooperate with the IAEA fully and without delay, and we look forward to additional reporting from the IAEA in the coming weeks on the steps taken by Iran.