ABU DHABI, United Arab Emirates -- Iran's nuclear deal with world powers may hang in the balance, but you wouldn't know it at the United Nations conference on atomic energy held Monday in the United Arab Emirates.

Iran decided to skip the Abu Dhabi conference, leaving its seats empty as Yukiya Amano, the head of the International Atomic Energy Agency, avoided speaking about the nuclear deal at all in his address at the venue.

Officials at the Atomic Energy Organization of Iran did not respond to a request for comment from The Associated Press. The semi-official Tasnim news agency quoted an anonymous source at the organization late Monday saying the delegation could not attend as the UAE did not grant them visas.

At a later news conference, Amano himself declined to discuss it.

"This conference is open to all the countries and we welcome the participation of all the countries," Amano said. "But of course it depends on each country whether to attend or not. I do not comment on Iran's participation. It is (up to) Iran to decide."

During a visit to Iran the day before, Amano told reporters that Tehran was still honouring the 2015 nuclear accord. President Donald Trump has declined to re-certify the 2015 nuclear deal, sending it to Congress to address.

Both the UAE and neighbouring Saudi Arabia remain highly suspicious of the nuclear deal, which saw economic sanctions on Iran lifted in exchange for it limiting its enrichment of uranium. The two Gulf Arab countries say that new money flowing into Iran has aided its ability to back Shiite militias in Iraq and support embattled Syrian President Bashar Assad.

Also sharing that suspicion is Israel, which sent a delegation to the nuclear conference. The UAE, like many Arab countries, does not have diplomatic ties with Israel and remains opposed to its occupation of lands Palestinians want for a future state.

Conference organizers asked journalists not to film the Israeli delegation.

Israeli officials did not immediately respond to a request for comment. Their presence also nearly created a unique diplomatic conundrum, as conference organizers had seated them next to Iran.

Trump's refusal this month to re-certify the agreement has sparked a new war of words between Iran and the United States, fueling growing mistrust and a sense of nationalism among Iranians. The European Union, Britain and other parties to the deal have all encouraged Trump to keep the accord in place.

Amano reiterated that Iran remains in compliance with the deal when pressed by reporters in Abu Dhabi on Monday. However, he demurred when asked to discuss what actions Trump could take in the future.

"We do not speculate," Amano said. "So I do not have any comments on the future action of the president of the United States."

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Associated Press writer Amir Vahdat in Tehran, Iran, contributed to this report.