The U.S. Treasury Department on Monday put an official of North Korea's Munitions Industry Department on its sanctions list for illegally earning valuta for the regime in Vietnam.

The move came five days after Pyongyang tested new short-range ballistic missiles and may be intended as a shot before the bow of the North Korean regime, which has threatened to boycott working-level denuclearization talks.

In a press release, the Treasury Department said it put Kim Su-il, a North Korean trading official in Vietnam working for the Munitions Industry Department, on its sanctions list.

"Treasury continues to enforce existing sanctions against those who violate United Nations Security Council resolutions... and evade U.S. sanctions on North Korea's unlawful nuclear and ballistic missile programs," the statement said. Kim "has violated UNSCRs and supports North Korea's weapons program."

He is the latest individual to be sanctioned some seven months after Choe Ryong-hae, North Korean leader Kim Jong-un's right-hand man.

Based in Ho Chi Minh City, Kim, who was born in 1985, has played a role in helping the regime export mineral resources such as anthracite and titanium and import goods from Vietnam since 2016.

Meanwhile, U.S. Secretary of State Mike Pompeo stressed the need to resume talks with Pyongyang. "We hope that we can have working-level discussions starting again very soon, so that we can unlock the Rubik's Cube," Pompeo said at the Economic Club of Washington on Monday.

Asked about the possibility of lifting sanctions if the North stops production of additional nuclear weapons, he said, "We hope that there are creative solutions to unlocking this. It is a very difficult challenge for each of us."

"We have to remember, too, these aren't U.S. sanctions; these are UN Security Council resolutions," he added.