After ten days of airstrikes initiated by Israel aimed at crippling Iran’s nuclear programme which have led to deadly daily exchanges of missile fire between Tehran and Tel Aviv, the UN chief said that diplomacy must now prevail.

“We now risk descending into a rathole of retaliation after retaliation,” he said, responding to the US intervention overnight in support of Israel’s military campaign, which targeted three facilities involved in uranium enrichment.

Return to serious negotiations essential

“We must act – immediately and decisively – to halt the fighting and return to serious, sustained negotiations on the Iran nuclear programme,” Mr. Guterres added.

He told ambassadors the citizens of the wider Middle East region could not endure yet another cycle of destruction. Demanding a ceasefire, he also put Iran on notice that it must “fully respect” the Non-Proliferation Treaty on the development of nuclear weapons as a cornerstone of peace and security worldwide.

Iran has consistently denied the allegation from Israel and others that its ambitions are to become a nuclear armed State, versus developing atomic energy for purely peaceful purposes.

Israel, the US and Iran face a stark choice. “One path leads to a wider war,” the UN chief continued, “deeper human suffering and serious damage to the international order. The other leads to de-escalation, diplomacy and dialogue.”

Grossi warns of major risks following strikes

The head of the UN’s atomic energy watchdog, the IAEA, warned ambassadors the recent military strikes by Israel and now the US on nuclear sites in Iran have badly compromised safety and could pose serious risks if the situation worsens.

International Atomic Energy Agency Director General Rafael Grossi said the attacks had caused “a sharp degradation in nuclear safety and security”, even though there had been no radiation leaks which could potentially impact the public so far.

The IAEA chief warned ambassadors that if the short window of opportunity to return to dialogue closes then the destruction could be “unthinkable” while the global nuclear non-proliferation regime “as we know it could crumble and fall.”

Mr. Grossi confirmed that Iran’s main enrichment facility at Natanz had suffered major damage, including to key power infrastructure and underground halls containing uranium materials.

He said the main concern inside the site was now chemical contamination, which can be dangerous if inhaled or ingested.

Massive radiation leak still possible

He also listed damage at other nuclear-related sites across the country, including Esfahan, Arak and Tehran, adding that while radiation levels outside remained normal, the attacks had raised alarm over Iran’s operational nuclear plant at Bushehr.

Mr. Grossi warned that any strike on Bushehr could trigger a massive radiation release across the region. “The risk is real,” he said. “Military escalation threatens lives and delays the diplomacy that’s needed to resolve this crisis.”

He urged all sides to show restraint and said the IAEA stood ready to send experts back in to help monitor and protect damaged nuclear sites.

Senior political affairs official: ‘No military solution’

Assistant Secretary-General for Political Affairs Miroslav Jenča told ambassadors that the world is facing “a dangerous moment” following the US bombing mission, as Iran considers potential retaliation.

He warned the council that the region risks being “engulfed in further instability and volatility”, with “no military solution to this conflict”.

Mr. Jenča confirmed extensive damage at Iranian sites, citing open-source satellite imagery and Iranian reports that tunnels and buildings at the Fordow nuclear facility had been hit. He urged Tehran to grant IAEA inspectors access “as soon as safety conditions allow”.

Death toll mounting

Hostilities between Iran and Israel are now into their tenth day, and Mr. Jenča said the humanitarian toll is mounting. “Most [of the 430 killed in Iran] have been civilians,” he noted, while also citing Israeli reports of 25 dead and over 1,300 injured.

He also flagged growing threats from non-State armed groups, including the Houthis in Yemen, warning that their retaliation could widen the conflict. Iran’s parliament, meanwhile, has voiced support for closing the crucial trading route through the narrow Strait of Hormuz.

“The world will not be spared from the ramifications of this dangerous conflict,” Mr. Jenča said, urging countries to act in line with international law and the UN Charter.