Deal or no deal? What is happening with the Iran US ceasefire

Just hours after the world welcomed news of a two-week ceasefire between the U-S and Iran - which would have seen the Strait of Hormuz open up passage of much of the globe's oil supply - the fragile truce appears to be at serious risk. Iran now says it will target any ships that attempt to cross the major shipping passage - blaming deadly Israeli attacks on Lebanon overnight, which the U-S says were not subject to the ceasefire pact. So what happens now? And what have Iran and the US actually agreed to?