A senior U.S. State Department official said on Wednesday that European Union fines on U.S. companies are the biggest source of friction in transatlantic economic relations, singling out the bloc's Digital Markets Act, which targets dominant tech platforms.

"The biggest single source of friction in the U.S.-EU relationship from an economic standpoint is the recurrent fines, very onerous punitive fines instituted on U.S. companies," Under Secretary of State for Economic Growth Jacob Helberg said on a call with journalists.

Helberg said Washington was concerned by reports that another round of fines could be imposed on U.S. companies in the near future. He was speaking during a visit to Europe to deepen economic ties, advance partnerships in emerging technologies and push for what Washington calls a fair regulatory environment.

Helberg said he had had productive talks with the European Commission, including on European companies that play an important role in global supply chains, an area he said could offer scope for closer transatlantic cooperation.

"I believe we would be moving a lot faster if we didn't also have to simultaneously address the sources of friction that directly stem from the DMA," he said.

Helberg said he would meet with executives at Dutch chip equipment giant ASML, Europe's most valuable firm, on Thursday. He declined to answer questions on whether the U.S. government is satisfied with current U.S.-Dutch controls on ASML's exports to China.