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WASHINGTON — The Interior Department’s top watchdog has referred an investigation into a possible conflict of interest by Interior Secretary Ryan Zinke to the Justice Department, according to a person familiar with the matter, a sign that the federal government is considering a criminal investigation of Mr. Zinke’s actions.

It is not known which investigation was referred to the Justice Department. Mr. Zinke is the subject of at least six known federal investigations into allegations of ethical misconduct or other policy violations.

However, the person familiar with the matter, who was not authorized to speak publicly, said it was highly likely that the investigation now being examined by the Justice Department was one involving a Montana land deal involving Mr. Zinke and the chairman of the energy giant Halliburton.

The Interior secretary has come under heightened scrutiny since the resignation in July of the Environmental Protection Agency administrator, Scott Pruitt, who stepped down after investigations revealed multiple violations of ethics rules and possibly of the law.