The U.S. will impose new sanctions on the Wagner mercenary group in Russia.

The United States has decided to designate the Russian private military group Wagner as a significant transnational criminal organization, the White House said on Friday, a move that will expand the number of nations and institutions that can be prevented from doing business with the company.

“Our message to any company that is considering providing support to Wagner is simply this: Wagner is a criminal organization that is committing widespread human rights abuses,” John Kirby, the White House national security spokesman, told reporters at a news briefing.

The new measures against the company, which is already under U.S. sanctions, will take effect next week. Designating Wagner as a transnational criminal organization will freeze the company’s assets in the United States and ban Americans from providing money, goods or services to the group.

Mr. Kirby said that Wagner, a mercenary force run by a close ally of President Vladimir V. Putin of Russia, has established itself as a “rival power center” to the Russian military, and added that the group’s founder, Yevgeny Prigozhin, has overseen the deployment of some 50,000 personnel to Ukraine, a number that largely comprises contractors and newly released convicts.

Wagner’s mercenaries have played a large role in the battle for eastern Ukraine and have also carried out military operations in Africa.

“Russia is searching for arms in foreign countries, including through Wagner,” Mr. Kirby said.

Mr. Kirby said that North Korean officials have denied providing arms to Wagner, and then displayed a photo that showed Russian rail cars traveling in November between the two countries. He said that American officials had referred the photos to the United Nations Security Council and that he expects additional sanctions to be placed against the company after the panel reviews evidence that United Nations resolutions were violated.

“While we assess that the amount of material delivered to Wagner has not changed battlefield dynamics in Ukraine,” Mr. Kirby said, “we expect that it will continue to receive North Korean weapons systems.”