They were mostly schoolchildren. A U.N. official described it as a “possible war crime” as bombs from what are believed to be Russian or Syrian government planes struck a school in the rebel-held Syrian province. At least 26 students and teachers are thought dead in the village of Hass, according to monitoring groups, though Syrian state TV reporting on the bombardment said only militants were killed. “It’s horrible. I hope we were not involved,” Russia’s U.N. ambassador said, as humanitarian groups predicted the death toll could rise.