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.
The origin of the attack is still unclear, the official added. But the official noted that the Organization for the Prohibition of Chemical Weapons also is reporting no independent information of chemical weapons use. The official wasn't authorized to speak publicly on the matter and spoke on condition of anonymity.
"We have no reason to believe that these allegations represent anything more than the regime's continued attempts to discredit the legitimate opposition and distract from its own atrocities committed against the Syrian people," State Department spokeswoman Victoria Nuland told reporters.
"We don't have any evidence to substantiate the regime's charge that the opposition even has CW (chemical weapons) capability," she added.
Syria's state-run news agency said 25 people were killed in the attack on the Khan al-Assad village in northern Aleppo province. It said 86 people were wounded, some in critical condition, and published pictures of children and others on stretchers in what appeared to be a hospital ward.
Russia, which has steadfastly supported Assad in Syria's civil war, backed Assad's assertion Tuesday.
The Russian Foreign Ministry said the rebel use of chemical weapons represented an "extremely dangerous" development in a conflict that has already killed 70,000 people. It said the rebels detonated a munition containing an unidentified chemical agent, but didn't give further details.
White House spokesman Jay Carney said the U.S. is looking carefully at all allegations, but said the Obama administration is "deeply skeptical" of any claims emanating from Assad's regime. He said President Barack Obama believes any chemical weapons use would be unacceptable.
"This is an issue that has been made very clear by the president to be of great to concern to us," Carney said, adding that if the Syrian regime does use such weapons, "there will be consequences."
Asked if Syria's chemical weapons stocks remained secure, Nuland declined to answer. She also refused to assess the opposition's counterclaims that the regime used chemical weapons, beyond saying the U.S. would investigate the allegations.
"We've been very clear about our concerns that as the Assad regime becomes increasingly beleaguered, it finds that the violence that it is using by conventional means is inadequate, including its barbaric use of scuds," she told reporters. "So we are quite concerned that they will resort to other weapons. We've made clear that this would constitute a red line for the United States."
Nuland said the U.S. was asking Russia to explain its accusation against the rebels, but dismissed the likelihood of Moscow producing any evidence.
"They appear to have taken the regime's word for it," she said.
Syria has one of the world's largest arsenals of chemical weapons and Washington has been on high alert since last year for any possible use or transfer of chemical weapons by Assad's forces. It feared that an increasingly desperate regime might turn to the stockpiles in a bid to defeat the rebellion or transfer dangerous agents to militant groups such as Lebanon's Hezbollah, which the Syrian government has long supported.
At the time, officials noted movement of some of the Syrian stockpiles but said none appeared to be deployed for imminent use. Still, Obama declared the use, deployment or transfer of the weapons to be his "red line" for possible military intervention in the Arab country.
U.S. officials say they've been closely monitoring Syria's unconventional weapons stockpiles and coordinating with allies in the region and beyond on possible contingency plans in the event the weapons are no longer secure. They've provided no indication that Syrian rebels seized some of the stockpiles or acquired such weaponry in recent months.