The United States ambassador to the United Nations accused Russia on Monday of “actively working to undermine the enforcement” of sanctions aimed at curtailing North Korea’s nuclear weapons program.

The ambassador, Nikki R. Haley, said Russia had blocked recent United Nations action aimed at strengthening controls over chemical and biological weapons technology and had resisted efforts to prevent North Korea’s development of intercontinental missiles.

The United States also has photographic evidence, Ms. Haley said, of Russian vessels, including one named the Patriot, linking up with North Korean tankers on the high seas and illegally loading them with refined petroleum.

Ms. Haley made the accusations at a United Nations Security Council session that she had scheduled. She is the 15-member Council’s president for September.