Iranian Revolutionary Guard gunboats fired on a tanker in the Strait of Hormuz on April 18, reversing Iran's declaration the previous day that it was reopening the waterway. Iran reimposed control over the strait in response to Trump's decision to maintain a US blockade of Iranian ports despite Iran's agreement to allow commercial shipping during the ceasefire. The reversal escalates tensions just days before the April 22 ceasefire deadline and threatens global oil supplies that depend on the strait for roughly 20% of daily crude oil flow.