A U.S. official claimed that Russia has been shipping refined petroleum to North Korea at levels that violate the U.N. Security Council mandates, saying that Washington was mulling new sanctions in response.

The disclosure came on the first day after a U.N. panel of experts monitoring the enforcement of longstanding U.N. sanctions against North Korea for its nuclear weapons and missile programs was disbanded after a Russian veto.

"At the same time that Moscow vetoed the panel’s mandate renewal, Russia has been shipping refined petroleum from Port Vostochny to the DPRK (North Korea). Russian shipments have already pushed DPRK imports above the 500,000-barrel annual cap mandated by the U.N. Security Council," the U.S. official told Reuters, speaking on condition of anonymity.

The official said that in March alone, Russia shipped more than 165,000 barrels of refined petroleum to North Korea and that given the close proximity of Russian and North Korean commercial ports, Russia could sustain these shipments indefinitely.

Russia blocked the annual renewal of the panel in late March in what the U.S. official described as a calculated move by Moscow to hide its own violations of U.N. Security Council resolutions.

The official said the United States will continue to impose sanctions "against those working to facilitate arms and refined petroleum transfers between Russia and the DPRK."

"We have previously worked to coordinate autonomous sanctions designations with our partners - including Australia, the European Union, Japan, New Zealand, the Republic of Korea, and the United Kingdom - and we will continue to do so," the official said.

North Korea has been helping Russia in its war against Ukraine by supplying ballistic missiles.