The head of Iran's nuclear agency warned the United States on Tuesday against undermining the 2015 nuclear deal, saying international nonproliferation efforts as well as Washington's international standing would suffer as a result.

Iranian nuclear chief Ali Akbar Salehi told an international conference on enhancing nuclear safety that Washington's recent "delusionary negative postures do not augur well" for keeping the deal intact.

He said Iran didn't want to see the deal unravel but that "much more is at stake for the entire international community than the national interests of Iran."

U.S. President Donald Trump is set to deliver a speech on Iran this week in which he is expected to decline to certify Iran's compliance in the landmark 2015 agreement, referring it to Congress, and perhaps targeting the country's paramilitary Revolutionary Guard with new sanctions.

Salehi praised the progress that had been made since the 2015 deal, saying nonproliferation and disarmament efforts had benefited worldwide. He called it "simply too precious to be allowed to be undermined or weakened."

"The failure of the nuclear deal will undermine the political credibility and international stature of the U.S. in this tumultuous political environment," Salhehi warned.

He concluded that he hoped "common sense shall prevail."

The U.S. administration has faced two 90-day certification deadlines to state whether Iran is meeting the conditions needed to continue enjoying sanctions relief under the deal and has both times backed away from a showdown. But Trump more recently has said he does not expect to certify Iran's compliance with the October deadline looming.

On Monday, the European Union's foreign policy chief, Federica Mogherini, praised the 2015 deal as a "win-win" solution that was working.

"We settled a milestone for nonproliferation and we prevented a dangerous devastating military escalation," she told the conference via video message, adding that the International Atomic Energy Agency had certified Iran's compliance with the deal, including via inspections, eight times since it was signed.

She warned that with rising nuclear tensions on the Korean peninsula, "We have an interest and a responsibility and a duty to preserve the nuclear deal with Iran" and strengthening, not weakening the nonproliferation regime.

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This story has been corrected to give the word in Salehi's quote as "delusionary" instead of "illusory