International concern focused on fears that the unprecedented US attacks would deepen conflict in the volatile region after Israel launched a bombing campaign against Iran earlier this month.

Ali Akbar Velayati, an advisor to Iran's supreme leader Ayatollah Ali Khamenei, said bases used by US forces could be attacked in retaliation.

"Any country in the region or elsewhere that is used by American forces to strike Iran will be considered a legitimate target for our armed forces," he said in a message carried by the official IRNA news agency.

"America has attacked the heart of the Islamic world and must await irreparable consequences."

President Donald Trump urged Iran to end the conflict after he launched surprise strikes on a key underground uranium enrichment site at Fordo, along with nuclear facilities in Isfahan and Natanz.

"We had a spectacular military success yesterday, taking the 'bomb' right out of their hands (and they would use it if they could!)" he said on social media.

And while the US president did not directly advocate regime change in the Islamic republic, he openly played with the idea -- even after his aides stressed that was not a goal of American intervention.

"It's not politically correct to use the term, 'Regime Change,' Trump posted on his Truth Social platform. "But if the current Iranian Regime is unable to MAKE IRAN GREAT AGAIN, why wouldn't there be a Regime change??? MIGA!!!"

Defense Secretary Pete Hegseth told a Pentagon press briefing earlier that Iran's nuclear program had been "devastated," adding the operation "did not target Iranian troops or the Iranian people."

Standing beside Hegseth, top US general Dan Caine said that while it would be "way too early" for him to determine the level of destruction, "initial battle damage assessments indicate that all three sites sustained extremely severe damage and destruction."

Israel's Prime Minister Benjamin Netanyahu meanwhile said his country's military strikes will "finish" once the stated objectives of destroying Iran's nuclear and missile capabilities have been achieved.

"We are very, very close to completing them," he told reporters.

As Iran's leaders struck defiant tones, President Masoud Pezeshkian also vowed that the United States would "receive a response" to the attacks.

People gathered Sunday in central Tehran to protest against US and Israeli attacks, waving flags and chanting slogans.

In the province of Semnan east of the capital, 46-year-old housewife Samireh told AFP she was "truly shocked" by the strikes.

"Semnan province is very far from the nuclear facilities targeted, but I'm very concerned for the people who live near," she said.

In an address to the nation hours after the attack, Trump claimed success for the operation, and Vice President JD Vance followed up Sunday morning.

"We know that we set the Iranian nuclear program back substantially last night," Vance told ABC.

But he also suggested Iran still had its highly enriched uranium.

"We're going to work in the coming weeks to ensure that we do something with that fuel," he said. "They no longer have the capacity to turn that stockpile of highly enriched uranium to weapons-grade uranium."

Another Khamenei advisor, Ali Shamkhani, said in a post on X that "even if nuclear sites are destroyed, game isn't over, enriched materials, indigenous knowledge, political will remain."

Rafael Grossi, director of the International Atomic Energy Agency (IAEA), told an emergency meeting of the UN Security Council that craters were visible at the Fordow facility, but no one had been able to assess the underground damage.

He added that attacks on nuclear facilities could cause radiation leaks, but the IAEA had not detected any.

Israel's military was checking results of the US raid on the deeply buried nuclear facility in Fordow, with a spokesman saying it was uncertain if Iran had already removed enriched uranium from the site.

The main US strike group was seven B-2 Spirit bombers that flew 18 hours from the American mainland to Iran. Trump said Sunday the planes had landed safely on US soil after the marathon mission.

A US Air Force B-2 stealth bomber returns after the US attacked key Iranian nuclear sites, at Whiteman Air Force Base, Missouri, US, June 22, 2025 in a still image from video. (Reuters/ABC Affiliate KMBC)

In response to the attack, which used over a dozen massive "bunker buster" bombs, Iran's armed forces targeted sites in Israel including Ben Gurion airport near Tel Aviv, with at least 23 people wounded.

Nine members of the Revolutionary Guards were killed Sunday in Israeli attacks on central Iran, local media reported, while three people were killed after an ambulance was also struck.

Israeli strikes on Iran have killed more than 400 people so far, Iran's health ministry said. Iran's attacks on Israel have killed 24 people, according to official figures.

The United Arab Emirates, Qatar and Oman, which had been mediating Iran-US nuclear talks, criticized the US strikes and called for de-escalation.

French President Emmanuel Macron on Sunday warned against an "uncontrolled escalation" in the Middle East, as he and his German and British counterparts called on Tehran "not to take any further action that could destabilize the region."