By Michael Hernandez</p> <p>WASHINGTON (AA) - The U.S. on Friday lashed out at the Syrian regime and its principal supporter, saying they "falsely" blamed rebels and extremist groups for conducting a chlorine attack in northwestern Aleppo last month. </p> <p>"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," State Department spokesman Robert Palladino said in a statement. </p> <p>Palladino said Washington has information indicating Russian and regime personnel were directly involved in what the U.S. is saying was a false-flag operation involving tear gas. It was intended to undermine confidence in an ongoing cease-fire agreement in nearby Idlib, Palladino said. </p> <p>"The United States is deeply concerned that pro-regime officials have maintained control of the attack site in its immediate aftermath, allowing them to potentially fabricate samples and contaminate the site before a proper investigation of it by the Organization for the Prohibition of Chemical Weapons," he said. </p> <p>"We caution Russia and the regime against tampering with the suspected attack site and urge them to secure the safety of impartial, independent inspectors so that those responsible can be held accountable," Palladino added. </p> <p>Palladino did not provide evidence he says the U.S. has to back up its assessment. </p> <p>SANA, Syria's official news agency, said Nov. 24 that Hayat Tahrir al-Sham launched a chemical attack in the al-Khalidiya area of Aleppo, which is under regime control, asserting that more than a hundred civilians were affected.</p> <p>Russia's Defense Ministry claimed the alleged chemical strike targeted northwestern rural Aleppo, with mortars being fired from the Idlib de-escalation zone.</p> <p>Russia said 120mm mortar shells containing chlorine were fired from the al-Buraykat district controlled by Hayat Tahrir al-Sham.