U.S. Ambassador to the United Nations Linda Thomas-Greenfield speaks during a press conference at the U.S. Embassy compound in Seoul, April 17. Yonhap

The top U.S. envoy to the United Nations said Wednesday that Washington will continue to work with South Korea and other countries to establish an alternative to the U.N. monitoring panel on North Korean sanctions.

North Korea has been under tightened U.N. sanctions due to its nuclear and missile programs, which call for, among other things, a ban on the country's exports of coal and other mineral resources to cut off North Korea's access to hard currency.

Late last month, Russia vetoed a resolution on extending the mandate of the Panel of Experts for monitoring the implementation of sanctions aimed at curbing the North's illicit weapons development. With China's abstention, the panel is now set to expire on April 30.

Ambassador Linda Thomas-Greenfield said it is "critical" to make sure independent and accurate reporting on North Korea stays in place, noting the dissolution of the expert panel does not mean a disbandment of the sanctions regime.

"We cannot allow the work that the Panel of Experts are doing to lapse," Thomas-Greenfield said in a press conference at the U.S. Embassy compound.

"That regime stays in place," she said. "I think we will eventually find a mechanism to continue to do that reporting."

Thomas-Greenfield said Russia and China will continue to try to block efforts to keep the monitoring alive because they are already breaking the sanctions regime by engaging in illegal trade with North Korea.

"I don't expect that they will cooperate, or agree with any efforts that we make to find another path, but that is not going to stop us from finding that path," she said.

The veto by Russia came amid concerns over its growing military ties with North Korea following the summit between North Korean leader Kim Jong-un and Russian President Vladimir Putin at Russia's Vostochny spaceport in September.

During a visit to the border region separating the two Koreas on Tuesday, Thomas-Greenfield hinted at "creative" and "out of the box" options being considered for a new sanctions monitoring mechanism, even outside of the U.N. system.

She made that point again Wednesday.

"In the conversations (with Seoul officials), we discussed options both inside and outside the U.N. system, in lockstep with our ROK and Japanese partners. We will continue to have these conversations in the days and weeks ahead," she said.

Thomas-Greenfield was the first U.S. envoy to the U.N. to visit South Korea since 2016.

Wrapping up a four-day trip to Seoul, she was to fly to Japan, the last leg of her two-nation Asia swing. (Yonhap)