U.S. Secretary of State Mike Pompeo said Friday that the enforcement of U.N. sanctions on North Korea was critical to the denuclearization of the Korean Peninsula.

His remarks came after the U.S. accused Russia of altering an independent U.N. report to cover up Moscow’s alleged violation of U.N. sanctions on North Korea.

“Russia has actively attempted to undermine the U.N. Security Council resolutions,” Pompeo said during a news conference, “by attempting to change the language” of a report that evaluates compliance with sanctions against Pyongyang.

Pompeo spoke with U.S. Ambassador to the United Nations Nikki Haley on Friday. A day earlier, Haley said Russia pressured the independent sanctions monitors to amend a report that was eventually submitted to the Security Council’s North Korea sanctions committee last month.

“The United States is as committed as ever to continuing to enforce those U.N. Security Council resolutions. We believe they are central to President [Donald] Trump’s efforts to convince [North Korean leader] Chairman Kim Jong Un that full, final denuclearization on the Korean Peninsula is necessary,” Pompeo said.

Both Russia and China are seen as having pushed for the council to ease sanctions on Pyongyang since the U.S.-North Korea summit in June.

Tech companies sanctioned

Thursday, Washington imposed sanctions on two information technology companies based in China and Russia for supporting Pyongyang’s nuclear and missile programs.

Washington is accusing the companies, located in Beijing and Moscow but controlled by Pyongyang, of moving illicit funds to North Korea.

“These actions are intended to stop the flow of illicit revenue to North Korea from overseas information technology workers disguising their true identities and hiding behind front companies, aliases and third-party nationals,” said Treasury Secretary Steve Mnuchin in an official statement.

The department designated the China-based China Silver Star, its North Korean CEO Jong Song Hwa and its Russia-based sister company Volasys Silver Star as such fronts.

The sanctions come at a time when the U.S. is maintaining pressure on the North Korean government in its negotiations to denuclearize the Korean Peninsula.