The White House says the U.S. hasn't yet come to the conclusion that Syrian President Bashar Assad has used chemical weapons even though close U.S. allies say he has.
White House spokesman Jay Carney says the U.S. is concerned about the reports and is looking for conclusive evidence. He says the U.S. supports a U.N. investigation into the alleged use of chemical weapons.
Israel, Britain and France have already concluded that Assad's government used chemical weapons last month in his battle against insurgent groups, increasing the pressure on the U.S. and other countries to intervene.
During a trip to Israel last month, Obama warned that the use of chemical weapons would be a "game changer" requiring action from the international community.
Carney wouldn't say Tuesday what that action would be.