The United States labeled the Russian mercenary group Wagner a "transnational criminal organization" and pledged to impose additional sanctions on Friday.

Wagner "is a criminal organization that is continuing committing widespread atrocities and human rights abuses," White House national security spokesperson John Kirby said, adding that the Biden administration will impose economic penalties on the organization and its "support network" next week.

"These actions recognize the transcontinental threat that Wagner poses, including through its ongoing pattern of serious criminal activity," said Kirby.

"Our message to any company that is considering providing support to Wagner is simply this: Wagner is a criminal organization that is committing widespread atrocities and human rights abuses," he added.

Wagner has some 50,000 personnel deployed in Ukraine in order to bolster Russia's war effort there, according to U.S. assessments. The firm has been pivotal to Russia's recent gains in Donbass and has been involved in conflict worldwide, including in Libya, the Central African Republic and Mali.

On Thursday, Yevgeny Prigozhin, the group's leader, said his mercenaries "completely took control" of Kleshcheyevka, a key suburb of the city of Bakhmut through which Ukrainian troops had been supplied with weapons and military equipment.

Prigozhin claimed "fierce battles" continued around Kleshcheyevka, with the Ukrainians "clinging onto every meter of ground."

"Contrary to various opinions that the AFU (armed forces of Ukraine) is fleeing from Artyomovsk (Russian name for Bakhmut), this is not the case. The AFU works clearly, smoothly. We have a lot to learn from them. But in any case, the units of the Wagner PMC are moving forward meter by meter. The settlement of Artyomovsk will be taken," he said.