MOSCOW, Dec 12 (Reuters) – Russian state oil and gas revenue is likely to almost halve in December compared with ​a year ago to 410 billion roubles ($5.17 billion) as a ‌result of lower crude prices and a stronger rouble, Reuters calculations showed on Friday.

For ‌the entire year, the revenue is set to fall by almost a quarter to 8.44 trillion roubles, below the Finance Ministry’s 8.65 trillion rouble forecast, according to the calculations based on data from industry ⁠sources and official statistics ‌on production, refining and supplies.

Russia reported the lowest monthly oil and gas revenues of 405 billion roubles in ‍August 2020, when oil prices tumbled during the COVID-19 pandemic.

Oil and gas revenue is the number one source of cash for the Kremlin, making up ​a quarter of total federal budget proceeds. The decline is ‌painful for Russia, which has heavily boosted defence and security spending since launching its military campaign in Ukraine in February 2022.

Ukraine and its Western backers have repeatedly said they want to force Russia, the world’s second-largest oil exporter, to stop its war by undermining its ⁠economy.

The Finance Ministry had initially expected ​10.94 trillion roubles in oil and gas ​revenues this year, but revised down its forecast in October to account for declining global oil prices, which ‍have been falling, ⁠pressured by worries over a supply glut.

In November, the price of Russian oil in roubles used for tax purposes slumped 17.1% ⁠from October to 3,605 roubles per barrel.

The Finance Ministry will publish its oil ‌and gas revenue estimates for Decemberon January 14.

($1 = 79.3000 ‌roubles)

(Reporting by ReutersEditing by Tomasz Janowski)