Israel stepped up airstrikes against Iranian missile launchers and factories and Iran retaliated across the Gulf region, disrupting energy supplies and travel.
As explosions rang out in Tehran and in Lebanon where Israel said it struck Hezbollah militants the American embassy in Saudi Arabia came under drone attack.
Four days into a war that President Donald Trump suggested would last several weeks but perhaps longer, hundreds of people have been killed, the vast majority in Iran, where information has been limited in part by an internet shutdown.
The spiralling nature of the war raised questions about when and how it would end. Trump seemed to leave open the possibility for more extensive US military involvement, telling the New York Post on Monday that he was not ruling out the possibility of boots on the ground.