The U.S. report says a preliminary assessment "determined that 1,429 people were killed in the chemical weapons attack, including at least 426 children."
The assessment "will certainly evolve as we obtain more information," it adds.
"Secretary Kerry seems to have been sandbagged into using an absurdly over-precise number," said Anthony Cordesman, former director of intelligence assessment at the U.S. Defense Department.
Now with the Center for Strategic and International Studies, he writes on the CSIS website, "Put simply, there is no way in hell the U.S. intelligence community could credibly have made an estimate this exact."
It's unclear whether "these figures really had an intelligence source," Cordesman said . "Some sources indicate they may have actually come from a Syrian source called the Local Coordination Committees (LCC)" -- a Syrian opposition group.
http://edition.cnn.com/2013/09/04/world/syria-us-evidence-chemical-weapons-attack/?hpt=hp_c1