The Israeli airstrike that targeted Hamas’s Gaza chief this month hit him as he attended a meeting of the group’s highest ranking militants, killing several important operatives and leaving a void in the top leadership of the U.S.-designated terrorist group, Hamas and Arab officials said. The airstrike killed Mohammed Sinwar, who was quietly buried days later, along with other top militants including Mohammad Shabana, the commander of the group’s Rafah brigade, the officials said. The Hamas leaders had gathered in a tunnel in the southern Gaza city of Khan Younis to discuss matters including their approach to cease-fire talks with...