TOKYO, Sept 18 (Reuters) - Japan's import of liquefied natural gas (LNG) from Russia has jumped by 49% in August to 0.59 million metric tons and supplies from the U.S. were down by 41% to 0.38 million tons, year-on-year, preliminary customs data showed on Wednesday.

Overall, LNG import by Japan, the world's second biggest super-cooled gas buyer after China, was up 1% to 5.7 million tons in August, year-on-year, the data showed.

The increase in Russian volumes in August was due to the timing of cargo arrival comparing to last year and was not driven by demand, an industry source told Reuters.

LNG imports from the Middle East, which includes Qatar and Oman, were up 11.4% to 0.78 million tons, the data showed, without providing country breakdown for the region.

"The annual contract volume through long-term contracts is fixed, and if equalized, the same amount of LNG is imported each year. Japan, along with many other countries, does not purchase Russian LNG on a spot basis," the source said.

Japan's industry ministry did not immediately reply to a Reuters request for a comment.

In July, LNG supplies from Russia were down by 64% to just 0.09 million tones, year-on-year, according to the earlier released customs data, which, according to the same source, was due to maintenance at the Sakhalin-2 LNG plant.

Overall, LNG import by Japan was up by 10.4% back then backed by increased volumes from Brunei, Malaysia, Oman and Indonesia.

(Reporting by Katya Golubkova and Yuka Obayashi; editing by David Evans)

((jekaterina.golubkova@thomsonreuters.com;))