With North Korea set to celebrate its most important holiday next week, the U.S. is concerned that Pyongyang “may be tempted to take another provocative action,” including a possible nuclear test.

“We, in cooperation and coordination with our allies and partners, are prepared to deal with whatever they may undertake, and I want to emphasize that we obviously hope that they will refrain from further provocation,” U.S. Special Envoy for North Korea Sung Kim said.

North Korea will celebrate the birth of the country’s founder, Kim Il Sung, on April 15. Kim is the grandfather of current dictator Kim Jong Un.

The isolated country has not conducted a nuclear test since September 2017, its sixth on record.

As Russia’s war in Ukraine exacerbates tensions between the Kremlin and the West, Kim said Russian and Chinese diplomats at the United Nations have obstructed any U.S. effort to condemn North Korea’s recent spate of missile launches — including the kind of long-range one that Russia and China used to condemn back in 2017.

“Unfortunately, I cannot report that we have had productive discussions with” China or Russia about a new U.N. Security Council resolution, Kim told reporters during a briefing Wednesday.

The two countries have blocked even a public statement from the U.N. Security Council condemning the 13 recent launches, per Kim, even though they violate multiple U.N. resolutions.

Still, the U.S. and its allies are pursuing a new resolution to condemn North Korea’s launches because “the Security Council needs to respond to these blatant violations of multiple Security Council resolutions,” Kim said. “This is about the credibility of the United Nations.”

Kim, who also serves as the U.S. ambassador to Indonesia, traveled to Washington this week, including to meet his Chinese counterpart Tuesday for a “very long and detailed discussion.”

He said despite Chinese opposition, he remains “convinced that Beijing shares our goal of the complete denuclearization of the Korean Peninsula.”

Part of the U.S. outreach to China on this issue is because North Korea has rejected all U.S. entreaties under the Biden administration.

“We have sent several messages, both public and private, inviting them to a dialogue without any conditions,” Kim told reporters, but North Korea has yet to respond, which Kim called “very disappointing.”

He declined to speculate on why, but said the COVID-19 pandemic could be one reason. North Korea “finds itself isolated in unprecedented ways and has shut itself off during the COVID pandemic. Only the resumption of diplomacy can break this isolation,” he said.

Instead, the U.S. has heard more fiery rhetoric from Kim Jong Un’s sister, Kim Yo Jong, who this week warned of a nuclear response if South Korea prepared to strike. Kim said the U.S. was “concerned” by the “provocative” comments.

With Biden’s North Korea policy going nowhere fast, Kim argued it is still having an important effect. While Pyongyang remains committed to perfecting its nuclear weapons program, U.S. sanctions and pressure “are constraining their progress,” he said.