TEL AVIV—As deaths from airstrikes on the Gaza Strip passed 100 and rockets continued to rain into Israel, Prime Minister Benjamin Netanyahu said international pressure wouldn't influence his assault against Hamas and all options were possible, including a ground invasion.

Sirens on Friday wailed through Israel's major cities warning of incoming rockets, and the country's military said it exchanged fire with Lebanon in an area believed to be controlled by the militant group Hezbollah.

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