The U.S. government is prosecuting a State Department expert on North Korea in a probe that appears to step into uncharted territory — by declaring that a journalist is committing a crime in disclosing leaked information.

It’s the latest case of the Obama administration investigating classified information improperly disclosed to reporters.

During the investigation of State Department adviser Stephen Kim, law enforcement officials obtained a search warrant for some private emails of James Rosen, the chief Washington correspondent for Fox News. Investigators also tracked Rosen’s comings and goings from the State Department.

Kim, who is awaiting trial, is accused of revealing secrets to the news organization. No charges have been filed against Rosen.

An FBI agent seeking the search warrant spelled out the government’s view of the journalist’s role, saying the reporter is a co-conspirator and that there is probable cause to believe that the reporter committed a violation of criminal law.

“We are outraged to learn today that James Rosen was named a criminal co-conspirator for simply doing his job as a reporter,” said Michael Clemente, Fox’s executive vice president for news. “In fact, it is downright chilling. We will unequivocally defend his right to operate as a member of what up until now has always been a free press.”

The Kim case is further along than a separate leak probe in which prosecutors secretly subpoenaed Associated Press phone records. AP President and Chief Executive Gary Pruitt said the government’s conduct has had a chilling effect on newsgathering.

In June 2009, Rosen reported that U.S. intelligence officials warned President Barack Obama and senior U.S. officials that North Korea would respond to a United Nations Security Council resolution condemning nuclear tests with another nuclear test.

The 2010 affidavit for a search warrant, first reported by The Washington Post, does not identify Rosen as “the reporter,” but he wrote the story at issue, and Fox News confirmed it was him on Monday.

The White House wouldn’t comment about tracking Rosen, citing an ongoing criminal investigation.

“The president believes it’s important that we find a proper balance between a need — absolute need — to protect our secrets and to prevent leaks that can jeopardize the lives of Americans and can jeopardize our national security interests on the one hand, and the need to defend the First Amendment and protect the ability of reporters to pursue investigative journalism,” White House spokesman Jay Carney said.

The Justice Department said improper disclosure of classified information to the press can pose a serious risk of harm to national security.