NEW ORLEANS — The Justice Department will escalate its crackdown on illegal foreign influence operations in the United States, a senior Justice Department official said on Wednesday, violations that prosecutors have targeted with renewed vigor in recent years.

Prosecutors plan to pursue more cases of covert foreign influence, John C. Demers, the head of the Justice Department’s national security division, said at a conference in New Orleans on white-collar fraud.

The move, one of the first significant initiatives under Attorney General William P. Barr, shows that the Justice Department has made a priority one of the targets pursued by the special counsel, Robert S. Mueller III: potential violations of the Foreign Agents Registration Act, or FARA, which requires lobbyists and others to disclose any work they do to further the interests of foreign governments. Prosecutors had for decades mostly ignored such violations as lobbyists accepted millions of dollars from other nations.

Mr. Demers said that the department was overhauling its FARA enforcement unit and would assign Brandon L. Van Grack, a former prosecutor on Mr. Mueller’s team and a deputy chief in the national security division’s counterespionage unit, to oversee it. The new role shows that the department has shifted “from treating FARA as an administrative obligation and regulatory obligation to one that is increasingly an enforcement priority,” Mr. Demers said.