The US and Israel have launched an attack on Iran, with the first apparent strike landing near the offices of Supreme Leader Ayatollah Ali Khamenei.
Iranian media reported strikes nationwide, and smoke could be seen rising from the capital.
US President Donald Trump said in a video posted on social media that the US had begun “major combat operations in Iran”.
It was not clear whether 86-year-old Mr Khamenei was in his offices at the time. He has not been seen publicly in days as tensions with the US have grown.
The attack came after the US assembled a vast fleet of fighter jets and warships in the region to try to pressure Iran into a deal over its nuclear programme.
Roads to Mr Khamenei’s compound in central Tehran had been shut by authorities as other blasts rang out across the capital.
Neighbouring Iraq also closed its air space, according to the Ministry of Transport.
Targets in the Israeli campaign included Iran’s military, symbols of government and intelligence targets, according to sources.
Mr Trump wanted a deal to constrain Iran’s nuclear programme, and he sees an opportunity while the country is struggling at home with growing dissent following nationwide protests.
After the attacks on Saturday morning he appealed to the Iranian people to “take over your government — it will be yours to take”.
Tehran had hoped to avert a war, but maintains it has the right to enrich uranium and does not want to discuss other issues, like its long-range missile programme or support for armed groups like Hamas and Hezbollah.
Iran had warned that American military personnel and bases across the region would be targets for any retaliation.
Israeli defence minister Israel Katz described the attack as being done “to remove threats”.
Several hospitals in Israel launched emergency protocols, including moving patients and operations to underground facilities.
In Tehran, witnesses heard the first blast by Mr Khamenei’s office. State television later reported on the explosion, without offering a cause.
Sirens sounded across Israel at the same time as it closed its air space. The Israeli military said it had issued a “proactive alert to prepare the public for the possibility of missiles being launched toward the state of Israel”.
More explosions struck Iran’s capital after Israel said it was attacking the country. Authorities have offered no casualty information.
Meanwhile, Iran shut its air space and mobile phone services were cut.