A senior Israeli military intelligence analyst said pictures indicate the chemical weapons were used against civilians in a March attack on Aleppo.
Brig. Gen. Itai Baron, head of the research division at Military Intelligence, said photographs of Syrian victims show foam coming from their mouths, leading military intelligence to this conclusion, Haaretz reported.
"To the best of our professional understanding, the regime has used lethal chemical weapons on a number of occasions, including the incident on March 19," he said.
Carney told reporters it is "important to do whatever we can to monitor, investigate and verify any credible allegations, given the enormous consequences for the Syrian people and given, as you said, the president's clear statement about the fact that chemical weapons use is unacceptable. It is precisely because of the seriousness of the use of chemical weapons and the seriousness with which the President made clear that that use would be unacceptable, that it is incumbent upon us and our partners to investigate thoroughly and validate or verify allegations of chemical weapons use. And we are obviously doing that."
Carney declined to speculate on what action would be taken if the allegations prove true.
Twenty-five people died and 86 were injured March 19 when there was an alleged chemical weapon attack on Aleppo. Syrian President Bashar Assad's regime blamed rebels for the attack, while rebels blamed the government, Russia Today reported.
The determination by Israel that chemical weapons were used could spur the United States to intervene in Syria's civil war, The New York Times reported.
Speaking from Jerusalem after the attack, President Obama called the use of chemical weapons a "red line for us."
"Once we establish the facts I have made clear that the use of chemical weapons is a game changer," he said.
"When you start seeing weapons that can cause potential devastation and mass casualties and you let that genie out of the bottle, then you are looking potentially at even more horrific scenes than we've already seen in Syria," Obama added. "And the international community has to act on that additional information."
Baron criticized the international community for failing to intervene in the Syrian fighting, Haaretz reported.
"The developments are certainly worrying ones: First the fact that chemical weapons have been used without any ... [international] response is a very worrying development and could certainly signal that such a thing is legitimate," he said.