WASHINGTON (AP) — The Obama administration flatly rejected a claim by Syrian President Bashar Assad’s government that the U.S.-backed Syrian rebels used chemical weapons on Tuesday, calling it a desperate attempt by a beleaguered regime to distract attention from its own ledger of atrocities in two years of civil war.

A U.S. official went further and said there was no evidence either side had used such weapons Tuesday in an attack in northern Syria, disputing a competing claim by rebels that it was regime forces who fired the chemical weapon. Spokespeople for the White House and the State Department rejected only the Assad regime’s charge.