KYIV, Jan 4 (Reuters) - Russia"s Gazprom has cut its daily volume of gas transit via Ukraine to Europe to about 50 million cubic metres (mcm), the lowest level since January 2020, the head of the the Ukrainian gas transmission system"s operator said on Tuesday. Sergiy Makogon wrote on Facebook that the current volume was much lower than the 109.6 mcm, which Gazprom booked according to Ukraine"s five-year gas transit contract with Russia signed in December 2019. "Gazprom does not inform about the reasons for the decrease in transit," he said. Gazprom did not respond to a request to comment. Kyiv said that Russia was cutting gas supply to Europe via Ukraine in order to create shortage in cold period when consumption increases and speed up certification of another pipeline - Nord Stream 2, which is ready to start operations and pump Russian gas to Europe bypassing Ukraine. Russia has said it met all its contractual obligations on gas exports. Relations between Ukraine and Russia plummeted after Russia"s annexation of Crimea in 2014 and the outbreak of the war in eastern Ukraine. Kyiv accuses Moscow of using energy as a weapon against Europe, which Moscow denies.