Israel has launched a daylight attack on Iran’s capital, with a cloud of smoke rising from the city’s central area.
The first apparent strike happened near the offices of Supreme Leader Ayatollah Ali Khamenei, and Iranian media reported strikes nationwide.
The US is participating, though the extent of its involvement was not clear, according to sources.
It was not clear whether 86-year-old Mr Khamenei had been in his offices at the time. He has not been seen publicly in days as tensions with the US have grown, but the attack comes after the US assembled a 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.
Targets in the Israeli campaign included Iran’s military, symbols of government and intelligence targets, according to an official.
Neighbouring Iraq also closed its air space after Israel launched the strikes targeting Iran.
US President Donald Trump had wanted a deal to constrain Iran’s nuclear programme, and sees an opportunity while the country is struggling at home with growing dissent following nationwide protests.
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.
It was not clear if Iran would immediately strike back, but it had warned that American military personnel and bases spread 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. Iranian state television later reported 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 from the strikes.
Meanwhile, Iran shut down its air space and mobile phone services were cut.