White House Confirms Syria's Use of Chemical Weapons A short time before we came on the air tonight the white house confirming what.S. Authorities long suspected, that syria's president has used chemical weapons on his own people. Jonathan karl tonight on the evidence and the bigger question how will president obama respond. Reporter: United states sat on the side lines but earlier this year president obama warned the syrian government that if they used chemical weapons they would be crossing a red line. I have made clear that the use of chemical weapons is a game changer. Reporter: Evidence including this video has mounted that the syrian government has used chemical weapons. Opposition groups provided video they claimed showed the after math of attacks. France and england claimed to have physical evidence of chemicals used. Now the white house says it agrees the syrian government has used chemical weapons, including sarin gas on opposition groups on a small scale multiple times over the past year. The white house says the chemical attacks have killed an estimated 100 to 150 people. David, that's a small percentage of the more than 90,000 killed in the syrian conflict but the white house said again today that that crosses clear red lines. So what does that mean going forward? Any hint from the house about possible reaction? It's not entirely clear. Sr. White house officials said today that the president has decided to increase support, military support for trusted elements of the syrian opposition but they wouldn't say what the support is or whether it would include sending arms to the rebels. Others called for a into fly zone but today the white house said that operation is risky and costly and wouldn't do much good. Reaction to be determined. Jon karl, thanks. Next here to the landmark