WASHINGTON (AP) - The U.S. on Friday accused forces backed by the Syrian government and Russia of firing tear gas at civilians and falsely claiming it was a rebel chemical weapons attack.

The incident occurred Nov. 24 amid fighting near the government-held city of Aleppo and reportedly left dozens injured. Syrian officials and state media at the time said rebels used poisonous gas in missiles fired on a neighborhood. The Russian Defense Ministry on Friday repeated the allegation, which the opposition has denied.

A State Department spokesman said the government of President Bashar Assad and Russia falsely accused opposition groups of a chlorine attack. Robert Palladino said the U.S. has "credible information" that pro-government forces likely fired tear gas.

He said Russian and Syrian personnel were involved and are using the attack as an opportunity to undermine confidence in a cease-fire in neighboring Idlib, an anti-government stronghold. He said officials have prevented an investigation of the site.

Britain echoed that assessment. "It is likely that this was either a staged incident intended to frame the opposition, or an operation which went wrong and from which Russia and the regime sought to take advantage," the Foreign Office said in a statement.

In response, the Russian Defense Ministry said Syria asked international inspectors to look into the matter and said it has provided evidence of the use of toxic agents by rebels backed by the west.

"It can't be excluded that the loud accusations made by the U.S. Department of State are also aimed at distracting global public attention from criminal actions of the U.S. military in eastern Syria, where U.S. warplanes have been barraging residential areas around Hajin, killing dozens of civilians daily," it said in a statement.

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