Israeli officials urged the U.S. to consider military action in Syria as Britain's Prime Minister David Cameron spoke out to back the U.S.’s claim that President Bashar al-Assad had used chemical weapons. The White House said on Thursday that Syria likely used chemical weapons, but U.S. officials emphasized that they are not 100 percent certain. President Obama has previously stated that the use of such weapons would be a “game changer” in determining whether or not to intervene in Syria's two-year-old civil war—which has claimed tens thousands of lives. The administration urged caution, and said they would need definitive proof before getting involved. Israel is threatening to strike Syria—anxious to stop weapons from Assad’s army from falling into the hands of Hezbollah militants in neighboring Lebanon.