The US said it was not involved and US President Donald Trump said Tehran cannot have a nuclear bomb after Israel said early on Friday it had struck Iranian nuclear targets to block that country from developing atomic weapons.
Iranian media and witnesses reported explosions including at the country's main uranium enrichment facility. The attack killed at least two top Iranian military officers, raising the potential for an all-out war between the two bitter Middle East adversaries. It appeared to be the most significant attack Iran has faced since its 1980s war with Iraq.
Calling it a "decisive moment in Israel's history," Israeli Prime Minister Benjamin Netanyahu said the country was also targeting Iranian scientists working on a nuclear bomb and missile factories in an operation that would continue for days.
Israel declared a state of emergency in anticipation of retaliatory missile and drone strikes by Tehran.
Iran has long maintained that its nuclear-related activity is for peaceful purposes.
Trump was equivocal on the talks with Tehran, telling Fox News: “Iran cannot have a nuclear bomb and we are hoping to get back to the negotiating table. We will see."
Here are some reactions from top officials and governments around the world:
US secretary of state Marco Rubio
"Tonight, Israel took unilateral action against Iran. We are not involved in strikes against Iran and our top priority is protecting American forces in the region."
"Let me be clear: Iran should not target US interests or personnel."
Australia: ‘Alarmed by the escalation between Israel and Iran’
"Australia is alarmed by the escalation between Israel and Iran,” foreign minister Penny Wong said. “This risks further destabilising a region that is already volatile. We call on all parties to refrain from actions and rhetoric that will further exacerbate tensions.
"We all understand the threat of Iran's nuclear and ballistic missile programme represents a threat to international peace and security, and we urge the parties to prioritise dialogue and diplomacy."
New Zealand: ‘That region does not need any more military action’
"It's a really unwelcome development in the Middle East,” Prime Minister Christopher Luxon said. “The risk of miscalculation is high. That region does not need any more military action and risk associated with that."
Japan: ‘Prevent further deterioration’
"Japan continues to make all necessary diplomatic efforts to prevent the further deterioration of the situation, while implementing every possible measure to ensure the protection of Japanese citizens," chief cabinet secretary Yoshimasa Hayashi said.
UN: ‘Condemn any military escalation in the Middle East’
"The Secretary-General condemns any military escalation in the Middle East. He is particularly concerned by Israeli attacks on nuclear installations in Iran while talks between Iran and the United States on the status of Iran's nuclear programme are underway,” the spokesperson for UN Secretary-General Antonio Guterres said.
"The Secretary-General asks both sides to show maximum restraint, avoiding at all costs a descent into deeper conflict, a situation that the region can hardly afford."
Oman: ‘Flagrant violation of UN Charter, international law’
Oman, which is mediating Iran-US nuclear talks, said it “considers this act a dangerous, reckless escalation, representing a flagrant violation of the United Nations Charter, the principles of international law. Such aggressive, persistent behavior is unacceptable and further destabilizes the regional peace and security.
"The Sultanate of Oman holds Israel responsible for this escalation and its consequences, and calls upon the international community to adopt a firm and unequivocal stance to halt this dangerous course of action."
(With inputs from agencies)