"Iran's key nuclear enrichment facilities have been completely and totally obliterated. Iran, the bully of the Middle East, must now make peace," President Donald Trump said in an address after the strikes.
Here is a roundup of the key reactions:
Iran
'Everlasting consequences' - Iran's Foreign Minister Abbas Araghchi condemned the US attacks as "outrageous" and said his country had a right to defend its sovereignty.
"The events this morning are outrageous and will have everlasting consequences," he posted on social media, calling the attacks "lawless and criminal" behaviour.
Araghchi later said the United States and Israel crossed "a very big red line" with the attacks, and said he would head to Moscow later Sunday for talks with President Vladimir Putin.
Israel
Israeli Prime Minister Benjamin Netanyahu congratulated Trump, saying the attacks would "help lead the Middle East and beyond to a future of prosperity and peace".
"Your bold decision to target Iran's nuclear facilities with the awesome and righteous might of the United States will change history," Netanyahu said in a video message, adding that the attacks demonstrated "America has been truly unsurpassed".
He also told Israelis that his promise to destroy Iran's nuclear facilities had been "fulfilled".
European Union
The European Union's top diplomat Kaja Kallas called for de-escalation and a return to negotiations.
"I urge all sides to step back, return to the negotiating table and prevent further escalation," Kallas wrote on X, adding that Iran must not be allowed to develop a nuclear weapon and that EU foreign ministers would discuss the situation Monday.
Russia
Russia "strongly condemned" the bombings, calling them "irresponsible" and a "gross violation of international law". "A dangerous escalation has begun, fraught with further undermining of regional and global security," the Russian foreign ministry added.
United Nations
UN Secretary-General Antonio Guterres called the strikes a "dangerous escalation in a region already on the edge".
"There is no military solution. The only path forward is diplomacy. The only hope is peace," Guterres said in a statement.
Britain
UK Prime Minister Keir Starmer called on Iran to "return to the negotiating table and reach a diplomatic solution to end this crisis".
"Iran can never be allowed to develop a nuclear weapon and the US has taken action to alleviate that threat," Starmer said on X, adding that "stability in the region is a priority".
France
French President Emmanuel Macron has called a meeting of the country's defence council for Sunday, with his office saying he had spoken with the leaders of Saudi Arabia and Oman on Sunday.
France is urging "all parties to exercise restraint to avoid any escalation that could lead to an extension of the conflict", Foreign Minister Jean-Noel Barrot posted on X.
China
China's foreign ministry said it "strongly condemns" the US strikes, warning that they "escalate tensions in the Middle East".
"China calls on all parties to the conflict, especially Israel, to cease fire as soon as possible," the ministry said.
Pope Leo XIV
Pope Leo XIV said after the strikes that "humanity is crying out for peace" and called for an end to all wars.
"Each member of the international community has the moral responsibility to end the tragedy of war, before it becomes an irreparable chasm," Leo said during his weekly Angelus prayer at the Vatican.
Saudi Arabia
Saudi Arabia expressed "great concern" after the strikes on its neighbour, the "sisterly Islamic Republic of Iran".
"The Kingdom underscores the need to exert all possible efforts to exercise restraint, de-escalate tensions, and avoid further escalation," the foreign ministry posted on X.
Pakistan
Pakistan, the only nuclear-armed Muslim country and a longtime Washington ally, said the US attacks "violate all norms of international law". "We are gravely concerned at the possible further escalation of tensions in the region," Pakistan's foreign ministry said, adding that Iran had the "right to defend itself under the UN Charter".
Hamas
The Palestinian resistance group Hamas condemned the "blatant US aggression against the territory and sovereignty of the Islamic Republic of Iran".
"This brutal aggression is a dangerous escalation," Hamas said, calling the attack "a flagrant violation of international law, and a direct threat to international peace and security".
Houthis
Yemen's Houthis, who are backed by Iran, condemned the US attacks and expressed solidarity with the Iranian people.
"The Trump administration's reckless aggression... is a blatant declaration of war against the brotherly Iranian people. We declare our full support for the brotherly Iranian people," it said.
