WASHINGTON, Oct 24 (Reuters) - The top law enforcement officials in the United States will on Monday announce U.S. action targeting "malign influence schemes and alleged criminal activity" by a "nation-state actor," the Department of Justice said.The national security cases will be discussed at a news conference at 1:30 p.m. (1730 GMT), the department said in a statement, without giving further details.U.S. Attorney General Merrick Garland, Deputy Attorney General Lisa Monaco and Assistant Attorney General for National Security Matthew Olsen along with FBI Director Christopher Wray will "discuss significant national security cases addressing malign influence schemes and alleged criminal activity by a nation-state actor in the United States," the department said.Register now for FREE unlimited access to Reuters.comThe Justice Department also did not cite whether the schemes involved or were aimed at the Nov. 8 midterm U.S. elections.Register now for FREE unlimited access to Reuters.comOur Standards: The Thomson Reuters Trust Principles."