WASHINGTON, Dec 12 (Reuters) - Russia is turning to decades-old ammunition with high failure rates as it burns through its stockpiles to carry out its nearly 10-month-old invasion of Ukraine, a senior U.S. military official said on Monday."They have drawn from (Russia's) aging ammunition stockpile, which does indicate that they are willing to use that older ammunition, some of which was originally produced more than 40 years ago," the official said, speaking on condition of anonymity.The senior U.S. military official assessed that Russia would burn through its fully-serviceable stocks of ammunition by early 2023 if it did not resort to foreign suppliers and older stocks.Barbara Woodward also said Britain was "almost certain that Russia is seeking to source weaponry from North Korea (and) other heavily sanctioned states, as their own stocks palpably dwindle."Iran last month acknowledged it had supplied Moscow with drones, but said they were sent before the war in Ukraine."