U.S. Ambassador to the United Nations Linda Thomas-Greenfield is planning to travel to Japan and South Korea this month to discuss responses to North Korea, diplomatic sources said Thursday.

She is considering making the trip on the week of April 14 to discuss with senior officials from Tokyo and Seoul about alternatives to a U.N. expert panel on checking the implementation of international sanctions against North Korea.

Russia vetoed on March 28 a U.N. Security Council resolution to extend the panel's mandate, forcing it to stop its activities at the end of this month.

Also on Thursday, Japan, the United States and South Korea co-hosted an informal U.N. Security Council meeting on cybersecurity. They accused North Korea of acquiring funds for its nuclear and missile development through cyberattacks.

The expert panel's latest report published last month said that "40% of the weapons of mass destruction programs of the Democratic People's Republic of Korea are funded by illicit cybermeans," using the official name of North Korea.