Israel says Iran has been firing cluster munitions throughout their 10-day war — adding a complicated and deadly challenge to Israel’s already stretched air defenses. The warheads burst open at high altitudes, scattering dozens of smaller bomblets across a wide area. The smaller bombs are difficult to intercept and have proven lethal. Normally restrictive about releasing information on Iranian hits and damage, Israeli authorities in recent days have publicized their dangers, which can persist as unexploded bombs on the ground even after civilians leave shelters. Over 120 countries have signed an international convention banning the use of cluster munitions, although Israel, the United States and Iran are among the nations that have not joined the treaty.