GENEVA (AP) — A UN panel looking into war crimes in Syria said Monday 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 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 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 chairman, Brazilian diplomat and scholar Paulo Sergio Pinheiro, said in the statement that the panel “reminds all parties to the conflict that the use of chemical weapons is prohibited in all circumstances under customary international humanitarian law.”

The United States says there is new evidence that Bashar’s regime used chemical weapons. The US has said intelligence indicates Syria has used the nerve agent sarin on at least two occasions, but 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.

The panel was appointed by the 47-nation Human Rights Council, the UN’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.

Lists of people suspected of human rights violations who could be prosecuted under international law are being kept secret by the UN’s top human rights official.

The panel’s next report to the UN Human Rights Council is on June 3.

Copyright 2013 The Associated Press.