CAIRO—An Egyptian court on Saturday sentenced ousted President Mohammed Morsi to death for breaking out of prison during the height of the nation’s uprising in 2011, the latest blow against Islamist critics of the government.

The decision is the harshest of multiple sentences given to Mr. Morsi and underscores the breadth of current President Abdel Fattah Al Sisi’s crackdown on his chief political opponents, the Muslim Brotherhood.

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