President Barack Obama did not address reports that chemical weapons had been deployed in Syria during a joint press conference Wednesday with Israeli President Shimon Peres, who expressed concern about the matter.
"Those weapons could fall into terrorist hands" and throw the region into greater crisis, Peres said, responding to reports that chemical weapons had been used in the Syrian city of Aleppo.
Israeli officials confirmed soon after Obama touched down in the region that such weapons had been used.
The Syrian government alleges that embattled rebel fighters used the chemical weapons, while the opposition maintains that it was Assad who deployed them near the city of Aleppo.
Use of such weapons would breach a so-called "red line" for the U.S., which said it could not determine whether chemical weapons had been used.
Israeli officials disagree.
"Israeli security officials believe chemical agents were used near Aleppo, but on a relatively small scale," the Israeli news site YNet reported. "However, the officials could not say who was behind the chemical attack—the rebels or Assad's regime."
"A Reuters photographer said victims he had visited in Aleppo hospitals were suffering breathing problems and that people had said they could smell chlorine after the attack," according to YNet.
U.S. and Israeli officials are concerned that Syria’s chemical weapons could fall into the hands of terrorists, many of whom are believed to have infiltrated Syrian opposition forces.
Israeli officials have warned for days that Assad was gearing up to use chemical weapons for the past week.
News of the alleged attack drew a pitched response in Congress, where many lawmakers are urging Obama to live up to his word and finally take action against Assad.
"President Obama has said that the use of weapons of mass destruction by Bashar Assad is a ‘red line’ for him that ‘will have consequences,’" Republican Sens. Lindsey Graham and John McCain said in a joint statement Wednesday. "If today’s reports are substantiated, the President’s red line has been crossed, and we would urge him to take immediate action to impose the consequences he has promised."