SEOUL, South Korea (AP) — The United States and its allies are discussing options “both inside and outside the U.N. system” to create a new mechanism for monitoring North Korea over its nuclear weapons program, the American ambassador to the United Nations said Wednesday.

Russia last month vetoed a U.N. resolution in a move that effectively abolished monitoring by U.N. experts of Security Council sanctions against North Korea, which prompted Western accusations that Moscow was acting to shield its arms purchases from North Korea to fuel its war in Ukraine.

“I look forward to engaging with both the Republic of Korea and Japan, but like-minded (countries) as well, on trying to develop options both inside the U.N. as well as outside the U.N. The point here is that we cannot allow the work that the panel of experts were doing to lapse,” U.S. Ambassador Linda Thomas-Greenfield told a news conference in Seoul, using the formal name for South Korea.