Iran and Israel traded missiles and air strikes on Saturday, the day after Israel launched a sweeping air offensive against Iran, killing commanders and scientists and bombing nuclear sites in a stated bid to stop it building an atomic weapon.

Iran said 78 people were killed on the first day and scores more on the second day, including when a missile brought down a 14-story apartment block in Tehran. Iran's retaliatory actions against Israel have left four people dead and more than 200 injured.

Iran has warned the United States, United Kingdom and France that their bases and ships in the region will be targeted if they help stop Tehran's strikes on Israel, Iran state media reported on Saturday.

UN Chief Antonio Guterres called on "both sides to show maximum restraint, avoiding at all costs a descent into deeper conflict, a situation that the region can hardly afford," according to a spokesperson.