Russia exported refined oil exports to North Korea in December for the first time in more than two years as the two countries forge closer ties following the invasion of Ukraine, United Nations data shows.

Russia reported to the UN that it shipped more than 67,000 barrels of refined petroleum products from December 2022 until April. It had last shipped 225 barrels of refined oil to North Korea in August 2020, the data shows.

Countries are required to report oil sales to the UN’s North Korea sanctions committee as part of measures imposed by the Security Council in 2017 after the pariah state carried out nuclear and long-range missile tests.

The aim of the measure was to “substantially reduce” oil supplies to North Korea as well as ban LNG exports. China continued to export oil to North Korea under the programme after Russia stopped its shipments.

Official oil product exports to North Korea are capped at 500,000 barrels per year under the UN scheme. Total exports have reached about one-fifth of that level so far this year based on exports from Russia and China, the figures show.

But that figure is believed to be much higher with a shadow fleet of vessels involved in shipping oil products to the peninsula.

Last year, the US offered a $5m reward for the arrest of a “fugitive” Singaporean shipowner who was accused of running an extensive scheme to avoid sanctions.

Kwek Kee Seng, who is said to have links to seven ships, was accused of acquiring the 3,912-dwt Courageous (built 1987) in 2019 and using it to carry gasoline to North Korea in defiance of US and UN sanctions.

The Courageous made ship-to-ship transfers to North Korean vessels and at least one direct shipment to the west coast port city of Nampo, the US said. Cambodian authorities seized the ship in March 2020.

Hours after the US alert, Singaporean authorities responded to say they knew where the shipowner was and that they had confiscated his passport.

North Korean President Kim Jong Un wrote to Vladimir Putin, his Russian counterpart, this week calling for a new era of strong relations between the two countries. The US has expressed concern that North Korea would send weapons to Russia in return for its oil.

“I think we would always be concerned with any country that is aligning with Russia to support its illegal, unjust invasion of Ukraine,” US State Department spokesman Matthew Miller said on Wednesday.