World leaders have urged calm after U.S. and Israeli strikes on Iran raised concerns about whether the violence could spread across the region and tensions rose with Iran vowing devastating blows after the killing of Iran’s Supreme Leader Ayatollah Ali Khamenei. On Sunday, a massive blast hit Iran’s capital as Israel said it targeted the “heart” of the city as Iran continued launching missiles at Gulf States. The killing of Ali Khamenei has deepened uncertainty. The United Nations and the European Union have pressed for talks, while countries are split over the strikes.