LONDON - President Barack Obama said the U.S. was still investigating claims that chemical weapons were used in Syria to determine if a "red line" had been crossed, reiterating that any such use would represent a "game-changer" in terms of U.S. action toward the Assad regime.

But Mr. Obama was clear that the facts of Tuesday's alleged chemical attack -- for which both the rebels and the regime traded blame -- had yet to be conclusively established, including whether it took place at all, despite some escalating rhetoric from within the U.S. and Israel.

Rep. Mike Rogers, R-Mich., chairman of the House Intelligence Committee, told "CBS This Morning" on Wednesday that there was a "high probability that a chemical agent was used in Aleppo."

"There has been some forensic evidence that at least small quantities may have been used in the past," said Rogers.

Israeli cabinet minister Yuval Steinitz echoed that sentiment Wednesday morning, calling it "apparently clear" that chemical weapons were recently used in Syria, just as Mr. Obama was due to touch down in Tel Aviv.

But if Rogers had information on forensic evidence, he didn't elaborate on it.

Others have been more cautious with their characterizations of Tuesday's incident. U.S. Ambassador to Syria Robert Ford told a House panel that the U.S. "no evidence to substantiate the reports that chemical weapons were used yesterday," And Rep. Dutch Ruppersberger, D-Md., who is the top-ranking Democrat on the House Intelligence Committee and has been briefed on the matter, wouldn't go as far as Rogers' "high probability" comment, saying only that he was "very concerned" about the reports.

The devil is in the details

CBSNews.com has spoken to two leading experts in chemical and biological weapons and warfare, and the clear consensus is that no chemical weapons have been used inside Syria.

"I am extremely skeptical that this [Aleppo strike] was a chemical warfare incident," said Jean Pascal Zanders, an expert in chemical and biological warfare with the European Union Institute for Security Studies.

Zanders said that images of victims in local hospitals and their descriptions of what they experienced left him with little doubt.

"The descriptions [of symptoms] would be totally, totally different to what we've been reading" if one of Syria's known chemical agents had been dispersed.

Syria is known to have significant stockpiles of Sarin gas, mustard gas and a variety of other military-grade agents, which attack the human respiratory and nervous systems.

There were many claims that a chlorine odor was present after the explosion in Khan al-Assal, and that victims suffered acute respiratory problems. There were even claims that some died of asphyxiation, but there was no evidence of dead bodies. In all, Zanders said evidence of a chemical weapons attack was very weak.

Rogers, however, was careful not to use the term "chemical weapons" on Wednesday. He said "chemical agents."