Syria and Russia on Wednesday accused the United States of lying about chemical weapons attacks in the Syrian conflict as a way of derailing efforts to bring an end to the fighting.

Syria’s state-run SANA news agency carried comments from a Foreign Ministry source condemning what it called “lies and allegations” by U.S. Secretary of State Rex Tillerson and French Foreign Minister Jean-Yves Le Drian.

Russian Deputy Foreign Minister Sergei Ryabkov told the Interfax news agency that whenever peace efforts advance, the United States promotes “rigged, unverified reports” of chemical weapons attacks in Syria.

Those comments came a day after the United States joined its NATO allies in launching a pressure campaign against the use of chemical weapons in Syria, while singling out Russia for protecting Syrian President Bashar al-Assad’s government.

“The recent attacks in East Ghouta raise serious concerns that Bashar al-Assad’s Syrian regime might be continuing its use of chemical weapons against its own people,” Tillerson said at a Paris conference hosted by Le Drian.