Last Updated 2:18 p.m. ET
The White House says it's highly likely that Syrian President Bashar Assad's regime, not the rebel opposition, was behind any chemical weapons use in Syria.
On Monday a U.N. panel looking into war crimes in Syria said it has not found conclusive evidence of chemical weapons use, backing away from a member's claims that there are indications rebel forces used the nerve agent sarin.
The commission "wishes to clarify that it has not reached conclusive findings as to the use of chemical weapons in Syria by any parties to the conflict," the panel said.
The U.N. statement comes after panel member and former war crimes prosecutor Carla Del Ponte told Swiss TV that the commission has indications Syrian rebel forces used nerve agent sarin as a weapon.
In the interview broadcast Sunday night, Del Ponte said the panel's investigators have "strong, concrete suspicions but not yet incontrovertible proof of the use of sarin gas from the way the victims were treated" - but no evidence government forces also used sarin as a chemical weapon.
She said the indications are based on interviews with victims, doctors and field hospitals in neighboring countries, though doubts were raised about her contention because the panel has mostly been interviewing refugees who oppose President Bashar Assad's regime.
"The U.N.'s inability to find a unified position on the Security Council on what to do about Syria, coupled with the failure of its Commission of Inquiry on the possible use of chemical weapons and the inability of its fact-finding mission to enter Syria, leaves diplomats wondering what, if anything, can bring an end to the bloody civil war that is increasingly expanding into a regional conflict," said CBS News' Pamela Falk from the United Nations.
At a press briefing today White House spokesman Jay Carney said there is certainly evidence that chemical weapons have been used, but that the U.S. is highly skeptical of claims that rebels put them in play.
Carney says the U.S. is still looking for conclusive evidence about chemical weapons use. He says there's no timeline for the investigation.
The U.N. panel was appointed by the 47-nation Human Rights Council, the U.N.'s top human rights body, to gather evidence on suspected war crimes and other abuses. It began its investigation in August 2011.
It has had almost no access to the ground in Syria, though earlier this year it said it had conducted at least 1,500 interviews and exhaustively corroborated its findings with other sources.
The United States has said intelligence indicates Syria has used the nerve agent sarin on at least two occasions, but President Obama has stressed that he needs more definitive proof before making a decision about how to respond - and whether to take military action.
Damascus denies using chemical arms, and says the opposition is trying to frame it.
Secretary of State John Kerry was leaving for Moscow on Monday to discuss the situation in Syria with Russian President Vladimir Putin.
The panel's next report to the U.N. Human Rights Council is on June 3.