World leaders urged peace and a return to talks as violence and tensions rose following the latest military attacks by the US and Israel and the killing of Iran's Supreme Leader Ayatollah Ali Khamenei.

A massive explosion from further Israeli airstrikes rocked Tehran on Sunday, while Iran pressed on with its retaliation campaign: Qatar, Kuwait and Bahrain said they intercepted a barrage of missiles.

Although US President Donald Trump vowed a huge fightback against retaliation, Iranian president Masoud Pezeshkian said: "The Islamic Republic of Iran considers bloodshed and revenge against the perpetrators and commanders of this crime as its legitimate duty and right, and will fulfill this great responsibility and duty with all its might."

The demise of Khamenei, who ruled for 36 years and has no designated successor, throws Iran's future into uncertainty and exacerbates already growing concerns of a broader conflict.

EU and China react

Top diplomats from the 27 European Union nations held an emergency meeting on Sunday to discuss the situation around Iran and the next steps for the bloc. 

The UN Security Council met late Saturday where the UN chief and many countries urged a halt to attacks and a return to negotiations to prevent the conflict from expanding further into the region and beyond.

Secretary-General António Guterres told the council that everything must be done to prevent an escalation. "The alternative," he warned, "is a potential wider conflict with grave consequences for civilians and regional stability."

Guterres said the US and Israeli airstrikes violated international law, including the UN Charter. He also condemned Iran's retaliatory attacks for violating the sovereignty and territorial integrity of Bahrain, Iraq, Jordan, Kuwait, Qatar, Saudi Arabia and the United Arab Emirates.

The Security Council meeting was tense as the US and Iranian ambassadors traded warnings and direct rebuffs.

Perhaps cautious about upsetting already strained relations with Trump, many nations, including several in the Middle East, refrained from commenting directly or pointedly on the joint strikes but condemned Tehran's retaliation.

China stated its opposition and condemnation of the US and Israeli offensives. A Foreign Ministry spokesperson said: "The attack and killing of Iran's supreme leader is a grave violation of Iran's sovereignty and security. It tramples on the purposes and principles of the UN Charter and basic norms in international relations. 

"We urge for an immediate stop to the military operations, no further escalation of the tense situation and joint effort to maintain peace and stability in the Middle East and the world at large."

Further calls for de-escalation came from across the Middle East and Europe.

"Return to your senses and deal with your neighbors with reason and responsibility before the circle of isolation and escalation widens," Anwar Gargash, an adviser to the United Arab Emirates' president, told the Iranian leadership on Sunday.

In recent years, the UAE sought to de-escalate tensions with Iran despite its longtime suspicions of its northern neighbor.

The 22-nation Arab League called the Iranian attacks "a blatant violation of the sovereignty of countries that advocate for peace and strive for stability." That coalition of nations has historically condemned both Israel and Iran for actions it says risk destabilizing the region.

With the EU meeting on Sunday, European Commissioner Ursula von der Leyen said: "With Khamenei gone, there is renewed hope for the people of Iran. We must ensure that the future is theirs to claim and shape. At the same time, this moment carries a real risk of instability that could push the region into a spiral of violence."

British Prime Minister Keir Starmer, French President Emmanuel Macron and German Chancellor Friedrich Merz called on the US and Iran to resume talks in a statement, saying they favored a negotiated settlement. The three countries have led efforts to reach a negotiated solution over Iran's nuclear program.

"We condemn Iranian attacks on countries in the region in the strongest terms. Iran must refrain from indiscriminate military strikes," they said. "Ultimately, the Iranian people must be allowed to determine their future."

Russian President Vladimir Putin condemned the American attacks, adding the death of Khamenei was a "murder" and was "committed in cynical violation of all norms of human morality and international law." 

Protests and celebrations

Thousands gathered in Tehran's main square to mourn the Iranian Supreme Leader. There were also reports of some celebrations in other parts of the country.

In Indian-controlled Kashmir, tens of thousands of people on Sunday staged massive demonstrations to denounce Khamenei's killing.

There were also demonstrations in other cities around the world, such as New York and Berlin, celebrating the end of Khamenei's rule.