AP
Obama will make the statement during a meeting with three world leaders — President Toomas Hendrik Ilves of Estonia, Dalia Grybauskaite of Lithuania, and President Andris Berzinš of Latvia. Vice President Joe Biden will also be at the meeting.
Obama's remarks will come after Secretary of State John Kerry's blistering statement earlier this afternoon, during which he called Syrian President Bashar al-Assad a "thug" and "murderer" and said he must be held accountable for a chemical-weapons attack earlier this month.