Russia has imported fuel from South Korean ports, easing the impact of a fuel crisis caused by Ukrainian drone strikes on Russian oil refineries, Ukraine's top sanctions official says.

More than 176,000 tonnes of petroleum products from South Korean ports in July and August were imported by Russia, Ukraine's top sanctions official Vladyslav Vlasiuk said on Tuesday.

The supplies from South Korea made up 31 per cent of Russian fuel imports in August, according to Mr Vlasiuk, citing what he said were reports that tankers, including ones under Western sanctions, were used for the deliveries.

"These shipments began precisely when Ukrainian strikes on Russian oil refineries were reducing processing volumes and creating a fuel shortage within Russia," Mr Vlasiuk, presidential commissioner for Ukrainian sanctions policy, wrote on Facebook.

His comments come amid a diplomatic row between Seoul and Kyiv that erupted last month when President Volodymyr Zelenskyy announced the transfer of two North Korean prisoners of war to South Korea, a step that Seoul says was meant to stay secret.

Ukraine has used long-range drones to attack Russian oil refineries and depots this year in what Kyiv has described as an effort to impose greater costs on its enemy, with no end in sight more than four years since Russia's full-scale invasion.

The strikes prompted Russia to impose a ban on diesel and gasoline exports, while restricting fuel purchases in some regions hit hard by the fuel crunch.

"In effect, imports from South Korea helped Russia offset the impact of losing its own refining capacity," Mr Vlasiuk said, citing "available data" and "reports" as sources in his post.

Earlier on Tuesday, the Guardian news agency reported that it had analysed port records and ship-tracking data, determining that the volumes were loaded at South Korean ports onto seven tankers, some of which are under UK and EU sanctions.

Mr Vlasiuk provided the same figures as those in the Guardian.

In response to the Guardian article, South Korea's Foreign Ministry said "the Korean government supports and actively participates in global efforts to end the war in Ukraine and achieve peaceful recovery".

It said that its government was strictly enforcing export controls against Russia by expanding the scope beyond strategic items to include "non-strategic items … that carry a high risk of diversion for military use."

Relations between South Korea and Ukraine have been under strain for weeks.

South Korean President Lee Jae Myung threatened unspecified measures against Ukraine on Friday unless Kyiv acknowledged a confidentiality agreement that Seoul says covered the transfer of two captured North Korean soldiers.

Seoul has said it wants an apology.

Ukraine denies there was a confidentiality agreement, but its foreign minister has said that Kyiv wants to mend ties with South Korea.

Reuters