MOSCOW--As Russian officials attack the U.S. over claims Syrian President Bashar al-Assad’s forces used chemical weapons, the country’s media have got themselves in a tangle over a false report that neatly fitted the government’s line.

Russian state agency ITAR-TASS published a report from Cairo Wednesday quoting a top United Nations official as saying it was Syrian rebels, not government forces, that used poison gas on Aug. 21. ITAR-TASS attributed quotes from Carla Del Ponte, a member of the UN’s commission looking into alleged gas attacks, to a Syrian news portal, which in turn was citing an interview on Swiss TV.

She was quoted as saying: “Evidence provided by eyewitnesses and people who suffered from a poisonous gas attack in the Eastern Ghouta region near Damascus obviously points to the fact that the neuro-paralytic gas sarin was used there by the paramilitaries of Syria’s irreconcilable opposition.”

The report was promptly matched by leading Russian news agency Interfax, this time from Beirut. It was quickly picked up by state-controlled TV and radio stations. The news appeared on almost every Russian news outlet, occupying lead spots on newspaper websites.

Russian politicians seized on the quote, which appeared to back up Russian government claims that rebels could have been responsible for the attack. Alexey Pushkov, a senior lawmaker from President Vladimir Putin’s United Russia party, accused Western press of deliberately ignoring Carla Del Ponte’s statement because it destroyed the basis for a military strike.