WASHINGTON, Jan 26 (Reuters) - The United States on Thursday stepped up sanctions against the Wagner Group, labeling the Russian mercenary company fighting in Ukraine as a transnational criminal organization responsible for widespread human rights abuses.

Wagner has been locked in a battle to take the towns of Bakhmut and Soledar in Ukraine's eastern Donetsk region, where Western and Ukrainian officials have said it is using convicts as cannon fodder.

The U.S. Treasury Department, as part of action targeting dozens of people and entities in an effort to degrade Russia's ability to wage the war, said it designated Wagner Group as a "significant transnational criminal organization" on Thursday.

"Wagner personnel have engaged in an ongoing pattern of serious criminal activity, including mass executions, rape, child abductions, and physical abuse in the Central African Republic (CAR) and Mali," the Treasury said in a statement.

It had previously designated Wagner under its Russia and Ukraine sanctions programs.

Russia's embassy in Washington did not immediately respond to a request for comment.

Washington also designated other entities it accused of supporting the Wagner Group's military operations, including Russia-based technology firm Joint Stock Company Terra Tech (Terra Tech), and targeted Russia's defense industrial complex.

Treasury designated China-based Changsha Tianyi Space Science and Technology Research Institute Co. LTD, known as Spacety China, accusing it of providing Wagner with radar satellite imagery over locations in Ukraine to Terra Tech.

"These images were gathered in order to enable Wagner combat operations in Ukraine," Treasury said.

A source told Reuters this week that the United States has determined that some Chinese companies are providing non-lethal assistance to Russia for use in Ukraine.

China's embassy in Washington did not immediately respond to a request for comment. A representative for Spacety China could not immediately be reached for comment.

"Today’s expanded sanctions on Wagner ... will further impede (Russian President Vladimir) Putin’s ability to arm and equip his war machine," Treasury Secretary Janet Yellen said in the statement.

White House national security spokesperson John Kirby last week said Putin has been increasingly turning to Wagner for military support, causing some tensions in Moscow.

He said the United States assesses Wagner has about 50,000 personnel deployed to Ukraine, including 40,000 convicts recruited from Russian prisons.

A Reuters investigation into recent burials in Southern Russia matched the names of at least 39 prisoners who have died for Wagner in Ukraine to Russian court records. They included a contract killer, murderers, career criminals, the news agency reported on Thursday.

Thursday's U.S. action is the latest raft of sanctions targeting Russia over its invasion of Ukraine, which has killed or wounded thousands and reduced cities to rubble.

Separately, the U.S. State Department on Thursday also designated entities and individuals with links to Wagner and its owner Yevgeny Prigozhin.

The State Department also targeted more of Vladimir Potanin's assets, tightening the screw on one of Russia's richest men, but stopping short of the jewel in his investment crown, mining giant Nornickel.

Last month the White House said Wagner had taken delivery of an arms shipment from North Korea to help bolster Russian forces in Ukraine, in a sign of the group's expanding role in that conflict.

North Korea's foreign ministry called the report groundless. Prigozhin denied taking delivery of arms from North Korea.