Vienna: The UN nuclear watchdog said it has been unable to establish contact with Iran’s nuclear regulatory authorities following the US-Israeli strikes, even as it stressed there was no evidence so far of damage to Iranian nuclear installations.

"Efforts to contact the Iranian nuclear regulatory authorities... continue, with no response so far. We hope this indispensable channel of communication can be re-established as soon as possible," Grossi said as he opened a special session on Iran of the board of governors of the International Atomic Energy Agency (IAEA).

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He added that the agency had “no indication” that any nuclear installations in Iran had been damaged or hit in the strikes.

However, Iran's ambassador to the UN nuclear agency alleged that US-Israeli airstrikes have targeted Iran's Natanz nuclear enrichment site.

Israel and the US have not acknowledged strikes at the site, which America bombed back in the 12-day war between Iran and Israel in June.

Iran's Ambassador to the International Atomic Energy Agency, Reza Najafi, told journalists he condemned what he called the "unlawful, criminal and brutal" attacks by the U.S. and Israel against Iran.

"Again they attacked Iran's peaceful, safeguarded nuclear facilities yesterday," Reza Najafi told reporters at a meeting. Asked by Reuters which facilities were hit, he replied, "Natanz."

Meanwhile, Grossi said the situation in the Middle East was "very concerning", urging "utmost restraint" after Israeli-US strikes on Iran and its retaliatory missile attacks.

"I reiterate my call on all parties to exercise maximum restraint to avoid further escalation," Grossi said as he opened a special session on Iran of the board of governors of the International Atomic Energy Agency (IAEA).

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Do Iran have nuclear weapons?

Iran does not currently possess recognised weapons of mass destruction and is a signatory to major international treaties that prohibit their development, testing, or stockpiling. These include the Nuclear Non-Proliferation Treaty (NPT), the Biological Weapons Convention (BWC), the Chemical Weapons Convention (CWC), and the Comprehensive Nuclear-Test-Ban Treaty (CTBT), all of which commit Tehran to renouncing WMD programmes.

The Iranian Red Crescent Society said Monday that the U.S.-Israeli airstrike campaign targeting Iran has killed at least 555 people so far in the Islamic Republic.

The society added that 131 cities have come under attack so far in the war.

The World Health Organisation called Monday for sparing civilians and healthcare facilities in the Middle East amid the escalating conflict.

“The protection of civilians and health care must be absolute,” Hanan Balkhy, regional dietitian at WHO wrote on social media. “All parties must … ensure medical facilities remain protected.”