It casts further doubts on a fragile ceasefire that went into effect on Thursday to stop the most intense fighting in the region in years.
The Israelis never officially confirmed the truce between Israel and Islamic Jihad, which was brokered by Egypt after a back-and-forth between Israel and the Palestinian militants claimed more than 30 lives in Gaza since Tuesday.
The violence began after targeted strikes by Israel killed two Islamic Jihad leaders, one of whom was the leader of the Quds Brigades, the armed wing of the Islamic Jihad in the Gaza Strip.
More than 450 rockets have been fired at targets across southern Israel since Tuesday, according to the Israeli army, with dozens being intercepted by the country's Iron Dome aerial defence system.
Islamic Jihad is the second-most powerful group in Gaza, after the coastal enclave's rulers, the Hamas movement, and has gained influence since 2014 with the help of financial backing from Iran.
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