The UN Security Council will hold an emergency meeting tonight following the US strikes against Iran's nuclear facilities, said Guyana, which holds the body's rotating chair for June.
The meeting, scheduled for 8pm Irish time, will be the Council's third since the Israel-Iran conflict began.
Earlier, UN Secretary-General Antonio Guterres called the strikes a "dangerous escalation in a region already on the edge."
"At this perilous hour, it is critical to avoid a spiral of chaos," Mr Guterres said in a statement.
"There is no military solution. The only path forward is diplomacy. The only hope is peace," he said.
Here is a roundup of the other key international reactions so far.
Iran: 'Everlasting consequences'
Iran's Foreign Minister Abbas Araghchi condemned the US attacks as "outrageous" and said his country has a right to defend its sovereignty.
"The events this morning are outrageous and will have everlasting consequences," he posted on X, adding that the attacks were "lawless and criminal" behaviour.
"In accordance with the UN Charter and its provisions allowing a legitimate response in self-defence, Iran reserves all options to defend its sovereignty, interest, and people," the foreign minister said.
Iran's atomic energy organisation also called the US attacks "a barbaric act that violates international law".
"The Atomic Energy Organization of Iran assures the great nation of Iran... it will not let the path of development of this national industry (nuclear), which is the result of the blood of nuclear martyrs, be stopped," it said in a statement published by state media.
Israel: 'Change history'
Israeli Prime Minister Benjamin Netanyahu congratulated Mr Trump, saying the attacks will "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," Mr 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".
Hamas: 'Brutal aggression'
Palestinian militant 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."
UK calls on Iran to return to negotiations
The British Prime Minister Keir Starmer said: "Iran's nuclear programme is a grave threat to international security. Iran can never be allowed to develop a nuclear weapon and the US as taken action to alleviate that threat.
"The situation in the Middle East remains volatile and stability in the region is a priority. We call on Iran to return to the negotiating table and reach a diplomatic solution to end this crisis."
EU vice president says 'step back'
European Commission vice president and high representative for foreign affairs and security policy, Kaja Kallas said that EU foreign ministers will discuss the situation tomorrow.
"Iran must not be allowed to develop a nuclear weapon, as it would be a threat to international security. I urge all sides to step back, return to the negotiating table and prevent further escalation," she said.
Democrats: 'Unilateral military action'
The top Democrat in the US House of Representatives accused Mr Trump of pushing the United States toward war.
"President Trump misled the country about his intentions, failed to seek congressional authorization for the use of military force and risks American entanglement in a potentially disastrous war in the Middle East," Congressman Hakeem Jeffries said in a statement.
"Donald Trump shoulders complete and total responsibility for any adverse consequences that flow from his unilateral military action".
The President's decision to bomb Iran was grossly unconstitutional, since only Congress has the power to declare war. The President’s action will without a doubt lead to many American, Israeli and Iranian deaths and must be condemned in the strongest possible terms.
— Rep. Nadler (@RepJerryNadler) June 22, 2025
'Grave concern'
"It is crucial that there be a quick de-escalation of the conflict. We are closely monitoring the situation there with grave concern," Japanese Prime Minister Shigeru Ishiba said.
The Australian government said that the security situation in the Middle East is "highly volatile".
"We have been clear that Iran's nuclear and ballistic missile program has been a threat to international peace and security. We note the US President’s statement that now is the time for peace.
"We continue to call for de-escalation, dialogue and diplomacy."
New Zealand's Foreign Minister Winston Peters described the situation in the Middle East as "extremely worrying".
"We acknowledge developments in the last 24 hours, including President Trump's announcement of US strikes on nuclear facilities in Iran. Ongoing military action in the Middle Eastis extremely worrying, and it is critical further escalation is avoided.
"New Zealand strongly supports efforts towards diplomacy. We urge all parties to return to talks. Diplomacy will deliver a more enduring resolution than further military action".
Humanity crying out for peace, pope says after US strikes Iran
Pope Leo XIV has reacted to the news of the United States striking nuclear sites in Iran by saying that "humanity is crying out for peace", and called for an end to wars.
"Each member of the international community has the moral responsibility to end the tragedy of war, before it becomes an irrepairable chasm," Pope Leo said during his weekly Angelus prayer at the Vatican, adding that he was reacting to the "alarming news coming from the Middle East".
