The Obama administration is challenging an Israeli intelligence assessment that Bashar al- Assad’s regime has attacked rebels with sarin or other toxic substances.

While the U.S. administration has said the the Syrian government’s use of chemical weapons would cross a “red line,” Secretary of State John Kerry and spokesmen from the White House and the Pentagon yesterday said American officials haven’t seen conclusive evidence that Syria’s government has deployed chemical weapons in that country’s civil war.

“We have not come to the conclusion that there has been that use,” White House spokesman Jay Carney told reporters in Washington. “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.”

Israeli General Itai Brun, chief of research and analysis for the army’s military intelligence division, cited photographic and other evidence yesterday indicating that Syria used chemical weapons last month near Damascus and Aleppo.