Prime Minister Benjamin Netanyahu vowed on Sunday to keep fighting in Gaza, even as anguish over the Israeli military's accidental killings of three hostages in the enclave raised new questions about how his government is prosecuting the war.Netanyahu, meanwhile, began a government meeting in Tel Aviv on Sunday by reading from a letter that he said came from families of Israeli soldiers killed fighting in Gaza. "You have a mandate to fight; you do not have a mandate to stop in the middle," Netanyahu read in Hebrew, according to a statement from his office.