The United States has urged countries to be diligent in maintaining sanctions on North Korea.
Pyongyang, meanwhile, says it is alarmed by recent U.S. attitudes, but remains committed to its nuclear deal.
U.S. Secretary of State Mike Pompeo called on countries Saturday to strictly enforce sanctions on the isolated nation. His remarks followed the release of a United Nations report warning that North Korea has found ways to navigate around the sanctions imposed over the North's nuclear weapons program.
Pompeo emphasized "the importance of maintaining diplomatic and economic pressure on North Korea to achieve the final, fully verified denuclearization that DPRK has agreed to," using the initials of the North's official name.
North Korean Foreign Minister Ri Yong Ho said his country "stands firm in its determination and commitment for implementing" the terms of denuclearization "in a responsible and good-faith manner."
The minister said, however, that recent U.S. attitudes are "alarming" and "go back to the old, far from its leader's intention."
The U.N. report said North Korea has had a "massive increase" of illegal ship-to-ship transfers of oil products at sea to evade sanctions.
The report also documented violations of a ban on North Korean exports, including coal, iron and seafood which generate millions of dollars of revenue for Pyongyang.
There are also indications that the North is continuing to build rockets and concerns that it has not been clear on when and how it will disarm.
Pompeo said the U.S. is taking any infringement of the sanctions very seriously.
"We have seen reports that Russia is allowing for joint ventures with North Korean firms and granting new work permits to North Korean guest workers," Pompeo said.
"If these reports are proven accurate, and we have every reason to believe that they are, that would be in violation "of U.N. sanctions." he said.
At a meeting of regional foreign ministers in Singapore Saturday, Pompeo and Ri approached each other during the "family photo," shook hands and exchanged a few words.
Pompeo said, "We should talk again, soon."
"I agree," Ri said. "There are many productive conversations to be had."
Following that exchange, the U.S. ambassador to the Philippines gave Ri a letter from President Trump to North Korea Chairman Kim. The White House said it was a response to a letter Kim had written to Trump earlier in the week.
Cindy Saine contributed to this report.