Russia doubled its oil product shipments to North Korea in the first half of this year over the same period last year, the Sankei Shimbun reported on Monday.

Russia has been a gaping loophole in international sanctions against the North.

Russia exported 4,304 tons of gasoline, diesel and other oil products to the North in the first half, which are valued at US$2.4 million, according to Russian customs statistics. The figure is about double the 2,171 tons it sent to the North in the first six months of last year.

There is speculation that the actual volume is much larger than the customs data reveal. Prof. Artyom Lukin of Russia's Far Eastern Federal University told the Japanese daily that Russia is estimated to be selling 200,000 to 300,000 tons of oil products to the North annually taking into account shipments sent via China.

He said Russian conglomerates may be ostensibly reluctant to do business with the North because of the U.S.-led international sanctions, but small firms will continue transactions.

Russia has so far blocked international efforts to cut off fuel supplies to the North.

