Russia and the United States traded blame over Syria's loss of Palmyra to the Islamic State (IS) extremist group for a second time over the weekend.
Russia blamed a lack of cooperation from the United States in fighting IS.
"There still is a lack of coordinated action and real cooperation with other states -- with the United States first and foremost," Kremlin spokesman Dmitry Peskov said on December 12. "This cooperation could allow us to avoid such attacks by terrorists."
Russian Foreign Minister Sergei Lavrov later suggested that, with IS fighters pouring into Palmyra as they flee a U.S.-backed Iraqi assault on Mosul, the development appeared orchestrated to distract Syrian forces from their battle to retake rebel-held parts of Aleppo.
"It makes me think, and I hope I am wrong, that it is all orchestrated...to give a respite to the bandits still in eastern Aleppo," Lavrov said.
But the Pentagon hit back, saying the Palmyra loss proved that Russia and Syria never gave any priority to battling IS extremists.
"It appears that Russia has failed to sustain the singular gain against ISIS they had achieved since their military intervention on behalf of the regime," Pentagon spokesman Major Adrian Rankine-Galloway told AFP.
"This is a further demonstration of why, as we have long advocated, Russia must change their focus."
Based on reporting by AFP and Reuters