Russia has resumed sending oil to sanctions-hit North Korea for the first time since 2020, deepening cooperation between the two nations that the US claims also includes sending arms from Pyongyang to help the Kremlin’s war in Ukraine.

A report released this week from a United Nations sanctions committee said Russia began sending refined petroleum products to North Korea in December 2022, which has continued into 2023. The shipments had been halted in about October 2020, the data showed, but Russia has sent about 67,000 barrels of oil since it restarted the flow.

The resumption of oil shipments comes as cooperation between the long-time partners has picked up in recent months, raising concerns that both nations may be evading sanctions in a partnership that helps North Korea’s beleaguered economy and funnels arms to Russian President Vladimir Putin for his attack on Ukraine.

Russia and North Korea appeared to have resumed trade over their sole rail link late last year, according to satellite images published by the 38 North website. The link had been closed in February 2020 when Kim Jong Un sealed his borders against the emerging Covid-19 threat. 

“We are concerned that the DPRK is planning to deliver more military equipment to Russia,” a US State Department spokesperson told Reuters on Tuesday, referring to North Korea by its official name. The State Department didn’t respond to a request for comment after normal business hours. 

The US in recent months has accused North Korea, which has backed Russia’s invasion, of sending arms and ammunition to aid Putin’s war, including shells and rockets. Pyongyang has dismissed the claims as groundless rumors.

One thing Kim’s regime has in abundance is weaponry, especially the Soviet-era artillery experiencing a revival on the frontlines of Ukraine. North Korea possesses stores of munitions to supply what the International Institute of Strategic Studies estimates is an arsenal of more than 21,600 artillery pieces, a force that has for decades held Seoul under the threat of devastation. 

While the Biden administration said the weapons won’t do much to alter the battlefield, the sales would open a stream of revenue to a North Korean state isolated from much of world trade.

Kim this week sent a message to Putin where he offered his support for the Russian people, saying he affirmed his willingness to “strive for closer strategic cooperation between the DPRK and Russia, holding hands firmly with the Russian president,” the official Korean Central News Agency reported. 

Any weapons sales would mark a reversal in roles between the neighbors, since North Korea for decades relied on weapons from its former benefactor, the Soviet Union. Pyongyang has been banned from arms sales for more than 15 years under UN resolutions that Russia helped impose, although the country still sells arms to the likes of Iran, Syria and Uganda, according to the US Defense Intelligence Agency.

North Korea is allowed to import 500,000 barrels of oil a year under the UN sanctions regime. But it has found ways to get around the measures, such as using ship-to-ship transfers of commodities on the high seas.