Israel’s military on Saturday defended soldiers who fired on Gazan protesters and said it was ready to respond with force again as demonstrations continued, raising prospects of a fresh conflict with Islamist movement Hamas.

At least 15 Palestinians died and more than 1,000 were injured Friday in clashes with Israeli soldiers, Palestinian authorities said, as tens of thousands of Gazans demonstrated on the Israeli border of the strip. Some protesters turned violent, drawing live fire from Israeli soldiers, the Israeli military...