UN Secretary-General Antonio Guterres on Sunday called US air strikes on nuclear facilities in Iran a "dangerous escalation in a region already on the edge."

"At this perilous hour, it is critical to avoid a spiral of chaos," Guterres said in a statement.

"There is no military solution. The only path forward is diplomacy. The only hope is peace."

The UN's nuclear agency also reported that it had not detected any increase in "off-site radiation levels" after the attacks on three nuclear sites in Iran. The agency's chief called for an emergency meeting on Monday.

Qatar, host of the biggest US military base in the Middle East, on Sunday said it feared serious repercussions after the attacks.

The foreign ministry "warns that the current dangerous escalation in the region may lead to catastrophic consequences at both the regional and international levels", a statement said.

"It calls on all parties to exercise wisdom, restraint, and to avoid further escalation."

Saudi Arabia likewise expressed concern.

"The Kingdom underscores the need to exert all possible efforts to exercise restraint, de-escalate tensions, and avoid further escalation," the Saudi foreign ministry posted on X.

Iraq, meanwhile, warned that the airstrikes threaten the entire region.

"This military escalation constitutes a grave threat to peace and security in the Middle East and poses serious risks to regional stability," said government spokesperson Basim Alawadi.

For his part, Israeli Prime Minister Benjamin Netanyahu congratulated US President Donald Trump on the attacks, saying they 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," 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."

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."

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 Iran must not be allowed to develop a nuclear weapon and that EU foreign ministers will discuss the situation on Monday.

Dmitry Medvedev, the deputy chairman of Russia's Security Council, said Trump had started a new war for the US by attacking Iran.

"Trump, who came in as a peacemaker president, has started a new war for the U.S.," Medvedev wrote on his Telegram channel.

The United States had carried out attacks on three nuclear sites in Iran on Sunday, with Trump warning Tehran it would face more devastating attacks if it does not agree to peace. (Agencies)