U.N. wants "unfettered access" to investigate alleged chemical weapons use in Syria

In this photo released by the Syrian official news agency SANA, a Syrian victim who suffered an alleged chemical attack at Khan al-Assal village according to SANA, receives treatment by doctors, at a hospital in Aleppo, Syria, Tuesday March 19, 2013. The U.S. has not found evidence that Syria has used chemical weapons.

UNITED NATIONS Secretary-General Ban Ki-moon announced Thursday that the United Nations will investigate the possible use of chemical weapons in Syria, which would be "a crime against humanity."

The U.N. chief said the investigation would look into the Syria government's allegation of an alleged chemical weapons attack, which Damascus blamed on rebels.

The rebels blamed regime forces for Tuesday's attack on Khan al-Assal village in northern Aleppo province and the Syrian National Coalition, the main opposition group, also demanded an international investigation.

The secretary-general said he was aware of "other allegations of similar cases involving the reported use of chemical weapons" but did not make clear whether these would be part of the investigation.

In Israel, President Obama said if Syria used chemical weapons in its civil war, as some reports suggested yesterday, that would be a "game changer" which -- officials have suggested in the past -- could cause the United States to take a more direct role in the conflict.

"The use of chemical weapons in Syria - and securing the weapons caches known to be held by the government - has become an increasing concern as the war widens to neighboring countries," said CBS News foreign affairs analyst Pamela Falk, "and it has become a focus of President Obama's trip to the Middle East."

Ambassador Susan Rice said in a statement that the U.S. welcomed the U.N. investigation.

"President Obama has been clear that the use or transfer of chemical weapons is totally unacceptable," Rice said. "If Bashar Al-Assad and those under his command make the mistake of using chemical weapons, or fail to meet their obligation to secure them, then there will be consequences. Those responsible will be held accountable."

France's U.N. Ambassador Gerard Araud said Wednesday that the Syrian National Coalition had alleged that there was a second chemical weapons attack on Tuesday in the Damascus area and it should be investigated as well.

Ban said he hopes the investigation "will contribute to ensuring the safety and security of chemical weapons stockpiles in Syria."

The secretary-general said the investigation will start "as soon as practically possible" but "will not happen overnight."

He said full cooperation from all parties will be essential and stressed that this includes "unfettered access."

Ban said his senior advisers are working to set up an investigation with the Organization for the Prohibition of Chemical Weapons which oversees the chemical weapons convention and the World Health Organization. He said issues to be decided include the overall mandate, the composition, and operational conditions including safety and security.

"My announcement should serve as an unequivocal reminder that the use of chemical weapons is a crime against humanity," the secretary-general said. "The international community needs full assurance that chemical weapons stockpiles are verifiably safeguarded."

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."

However, 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.

Leading experts in chemical and biological weapons and warfare told CBSNews.com that they believe there is no evidence that 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

CBS News correspondent David Martin reported that it's possible the victims in Aleppo were exposed to some other type of agent such as tear gas or an industrial chemical -- nasty stuff, but not a weapon of mass destruction. Still, that would be an ominous step toward chemical weapons.

Another expert told CBSNews.com that a far less sinister substance may be at the root of the current chemical weapons rhetoric: pesticide.

Hamish de Bretton-Gordon, an expert in chemical and biological weapons and the head of U.K. consultancy SecureBio, said that the culprit could well be organic phosphates, which he described as "the basis in all chemical weapons."