(CNN) The US and UK dismissed Russian and Syrian claims that opposition forces launched a gas attack on Aleppo in late November, saying that pro-Assad forces were responsible.

"On November 24, 2018, the Assad regime and Russia falsely accused the opposition and extremist groups of conducting a chlorine attack in northwestern Aleppo," Syria, State Department Deputy Spokesman Robert Palladino said in a statement. "The United States strongly refutes this narrative and has credible information that pro-regime forces likely used teargas against civilians in Aleppo on November 24."

'Highly unlikely'

A spokesman for the UK foreign office echoed the US denunciation. "We have seen nothing to support the claims made by Russia and Syria," the unnamed spokesperson said in a statement. "It is highly unlikely that the opposition was responsible."

Around 100 people were injured in the gas attack on Aleppo, according to Syrian state media and a British-based human rights group. It is not believed that chlorine was used in the attack, according to the foreign office.

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