WASHINGTON — The Justice Department will crack down on agents who are working to advance foreign agendas in the United States, Rod J. Rosenstein, the deputy attorney general, said on Thursday as he warned of a growing Russian threat to the United States.

Influence operations undertaken by foreign governments “are a form of information warfare,” Mr. Rosenstein said in a speech at the Aspen Security Forum in Colorado. “The Russian effort to influence the 2016 presidential election is just one tree in a growing forest.”

Mr. Rosenstein, whose remarks came as he delivered a report from the Justice Department’s cyberdigital task force, said that the government would step up enforcement of laws governing foreign agents and inform victims when they had been targeted in influence schemes.

His speech followed a week in which Russian influence was once again shown to have a transformative impact on modern American political life.