WASHINGTON (Reuters) - The U.S. State Department said on Saturday that Washington would not wait to impose sanctions on any shippers helping to get fuel to North Korea, in an apparent warning to Russia days after the U.S. ambassador to the United Nations accused Moscow of cheating on the measures.

North Korean leader Kim Jong Un speaks during joint news conference in Pyongyang, North Korea, September 19, 2018. Pyeongyang Press Corps/Pool via REUTERS

North Korea continues to employ tactics to evade U.N. sanctions, Heather Nauert, the State Department spokeswoman, said in a statement, adding that U.N. member states are required to prohibit ship-to-ship transfers of petroleum fuel to the hermit country.

“The United States will not hesitate to impose sanctions on any individual, entity, or vessel supporting North Korea’s illicit activities, regardless of nationality,” Nauert said.

The 15-member U.N. Security Council has unanimously boosted sanctions on North Korea since 2006 in a bid to choke funding for Pyongyang’s nuclear and ballistic missile programs.

But the United States and Russia have recently shown cracks in the unity of the council over the sanctions.

Washington has “evidence of consistent and wide-ranging Russian violations” of the sanctions, the U.S. ambassador to the U.N. Nikki Haley said on Monday. Russia was helping North Korea illegally obtain fuel through transfers at sea, had refused to expel a North Korean whom the Security Council blacklisted last year, and had pushed for changes to an independent U.N. report on sanctions violations to cover up breaches by Russians, she said.

Russia said after Haley’s comments that Moscow had not pressured the authors of the U.N. report and blamed Haley for heightening tensions.

With the warning on fuel shipments, the Trump administration signaled it was keeping pressure on Pyongyang even after saying there has been progress. President Donald Trump this week hailed a summit between North Korean leader Kim Jong Un and South Korean President Moon Jae-in, and said there had been “tremendous progress” with North Korea on several fronts including Pyongyang’s denuclearization.

Washington has tracked some 148 cases this year of tankers delivering fuel to North Korea in breach of a U.N. cap of 500,000 barrels a year. Haley has not said how many of those transfers may have involved Russia.

Both Russia and China have suggested the Security Council discuss easing sanctions after Trump and Kim met in June and Kim pledged to work toward denuclearization.

U.S. Secretary of State Mike Pompeo said on Friday the United States is working to set up another summit between Trump and Kim after their unprecedented meeting in Singapore, but there is still work to do.