By Parisa Hafezi, Phil Stewart and Maayan Lubell

ISTANBUL/WASHINGTON/JERUSALEM (Reuters) -The world braced on Sunday for Iran's response after the U.S. attacked key Iranian nuclear sites, joining Israel in the biggest Western military action against the Islamic Republic since its 1979 revolution.

Iran vowed to defend itself a day after the U.S. dropped 30,000-pound bunker-buster bombs onto the mountain above Iran's Fordow nuclear site while American leaders urged Tehran to stand down and pockets of anti-war protesters emerged in U.S. cities.

In a post to the Truth Social platform on Sunday, U.S. President Donald Trump raised the idea of regime change in Iran. "It’s not politically correct to use the term, 'Regime Change,' but if the current Iranian Regime is unable to MAKE IRAN GREAT AGAIN, why wouldn’t there be a Regime change??? MIGA!!!" he wrote.

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Iran and Israel continued to trade volleys of missile attacks. An Israeli military spokesperson said Israeli fighter jets had struck military targets in western Iran. Earlier, Iran fired missiles that wounded scores of people and flattened buildings in Tel Aviv.

The U.S. Department of Homeland Security warned of a "heightened threat environment" in America, citing the possibility of cyber attacks or targeted violence. Law enforcement in major U.S. cities stepped up patrols with a focus on religious, cultural and diplomatic sites.

The U.S. State Department issued a security alert for all U.S. citizens abroad that warned of the potential for demonstrations against Americans and travel disruptions due to closed airspace across the Middle East, calling on them to "exercise increased caution."

Tehran has so far not followed through on its threats of retaliation against the United States - either by targeting U.S. bases or trying to choke off global oil supplies - but that may not hold.

Speaking in Istanbul, Iranian Foreign Minister Abbas Araqchi said his country would consider all possible responses. There would be no return to diplomacy until it had retaliated, he said.

"The U.S. showed they have no respect for international law. They only understand the language of threat and force," he said.

Trump, in a televised address, called the strikes "a spectacular military success" and boasted that Iran's key nuclear enrichment facilities had been "completely and totally obliterated."

Commercial satellite imagery indicated the U.S. attack on Iran’s subterranean Fordow nuclear plant severely damaged or destroyed the deeply-buried site and the uranium-enriching centrifuges it housed, but the status of the site remained unconfirmed, experts said.

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The U.N. nuclear watchdog, the International Atomic Energy Agency, said no increases in off-site radiation levels had been reported after the U.S. strikes. Rafael Grossi, the agency's director general, told CNN that it was not yet possible to assess the damage done underground.

A senior Iranian source told Reuters that most of the highly enriched uranium at Fordow had been moved elsewhere before the attack. Reuters could not immediately corroborate the claim.

Satellite imagery from the U.S. space technology company Maxar Technologies showed a long line of vehicles waiting outside an entrance of the facility on Thursday and Friday.

Trump, who veered between offering to end the war with diplomacy or to join it before moving ahead with the biggest foreign policy gamble of his career, called on Iran to forgo any retaliation. He said the government "must now make peace" or "future attacks would be far greater and a lot easier."

In a step towards what is widely seen as Iran's most effective threat to hurt the West, its parliament approved a move to close the Strait of Hormuz. Nearly a quarter of global oil shipments pass through the narrow waters that Iran shares with Oman and the United Arab Emirates.

Iran's Press TV said closing the strait would require approval from the Supreme National Security Council, a body led by an appointee of Iran's Supreme Leader Ayatollah Ali Khamenei.

Attempting to choke off Gulf oil by closing the strait could send global oil prices skyrocketing, derail the world economy and invite conflict with the U.S. Navy's massive Fifth Fleet, based in the Gulf and tasked with keeping the strait open.

Brent crude and U.S. crude futures rose to the highest levels since January on Sunday, with Brent crude increasing $3.20 to $80.28 and U.S. crude $2.89 to $76.73.

U.S. Secretary of State Marco Rubio told CBS's "Face the Nation" that there were no other planned military operations against Iran "unless they mess around."

The U.N. Security Council met on Sunday to discuss the U.S. strikes as Russia, China and Pakistan proposed the 15-member body adopt a resolution calling for an immediate and unconditional ceasefire in the Middle East.

U.N. Secretary-General Antonio Guterres told the Security Council the U.S. bombings in Iran marked a perilous turn in the region and urged a halt to fighting and return to negotiations over Iran's nuclear program.

DIVERGING WAR AIMS

Israeli officials, who began the hostilities with a surprise attack on Iran on June 13, have increasingly spoken of their ambition to topple the hardline Shi'ite Muslim clerical establishment that has ruled Iran since 1979.

Israeli Prime Minister Benjamin Netanyahu told Israeli reporters that Israel was very close to meeting its goals of removing the threats of ballistic missiles and the nuclear program in Iran.

U.S. officials, many of whom witnessed Republican President George W. Bush's popularity collapse following his disastrous intervention in Iraq in 2003, have stressed that they were not working to overthrow Iran's government.

"This mission was not and has not been about regime change," Defense Secretary Pete Hegseth told reporters at the Pentagon, calling the mission "a precision operation" targeting Iran's nuclear programme.

Anti-war activists organized demonstrations on Sunday in New York, Washington and other U.S. cities, with signs carrying messages such as "hands off Iran."

Meanwhile, some Iranians said they feared the prospect of an enlarged conflict involving the U.S.

"Our future is dark. We have nowhere to go - it's like living in a horror movie," Bita, 36, a teacher from the central city of Kashan, said before the phone line was cut.

Much of Tehran, a capital city of 10 million people, has emptied out, with residents fleeing to the countryside to escape Israeli bombardment.

Iranian authorities say more than 400 people have been killed since Israel's attacks began, mostly civilians. Israel's bombardment has decimated much of Iran's military leadership with strikes targeted at bases and residential buildings where senior figures slept.

Iran has been launching missiles back at Israel, killing at least 24 people over the past nine days.

Air raid sirens sounded across most of Israel on Sunday, sending millions of people to safe rooms.

In Tel Aviv, Aviad Chernovsky, 40, emerged from a bomb shelter to find his house had been destroyed in a direct hit. "It's not easy to live now in Israel (right now), but we are very strong," he said. "We know that we will win."

(Reporting by Reuters; writing by William Mallard, Angus McDowall, Peter Graff, Raphael Satter and Ted Hesson; editing by Sonali Paul, Mark Heinrich, Nia Williams and Diane Craft)

Posted by: AAngeles