Israel launched a wave of airstrikes across the Gaza Strip, killing at least 200 people, in its heaviest assault since a ceasefire took effect in January. The strikes came after a lack of progress in talks to extend the ceasefire, and Prime Minister Benjamin Netanyahu said Israel would act against Hamas with increasing military strength. The surprise attack shattered a period of relative calm and raised questions about the fate of the remaining Israeli hostages held by Hamas. The renewed fighting threatens to reverse progress made in halting Gaza's humanitarian crisis.